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lines drawn to the point D, and less than twice the same, but greater than two-thirds of the lines drawn through the point to the opposite sides.
44. In a plane triangle an angle is right, acute or obtuse, according as the line joining the vertex of the angle with the middle point of the opposite side is equal to, greater or less than half of that side.
45. If the straight line AD bisect the angle A of the triangle ABC, and BDE be drawn perpendicular to AD and meeting AC or AC produced in E, shew that BD = DE.
46. The side BC of a triangle ABC is produced to a point D. The angle ACB is bisected by a line CE which meets AB in E. A line is drawn through E parallel to BC and meeting AC in F, and the line bisecting the exterior angle ACD, in G. Shew that EF is equal to FG.
47. The sides AB, AC, of a triangle are bisected in D and E respectively, and BE, CD, are produced until EF= EB, and GD=DC'; shew that the line GF passes through A.
48. In a triangle ABC, AD being drawn perpendicular to the straight line BD which bisects the angle B, shew that a line drawn from D parallel to BC will bisect AC.
49. If the sides of a triangle be trisected and lines be drawn through the points of section adjacent to each angle so as to form another triangle, this shall be in all respects equal to the first triangle.
50. Between two given straight lines it is required to draw a straight line which shall be equal to one given straight line, and parallel to another.
51. If from the vertical angle of a triangle three straight lines be drawn, one bisecting the angle, another bisecting the base, and the third perpendicular to the base, the first is always intermediate in magnitude and position to the other two.
52. In the base of a triangle, find the point from which, lines drawn parallel to the sides of the triangle and limited by them, are equal.
53. In the base of a triangle, to find a point from which if two lines be drawn, (1) perpendicular, (2) parallel, to the two sides of the triangle, their sum shall be equal to a given line.
54. In the figure of Euc. I. 1, the given line is produced to meet either of the circles in P; shew that P and the points of intersection of the circles, are the angular points of an equilateral triangle.
55. If each of the equal angles of an isosceles triangle be onefourth of the third angle, and from one of them a line be drawn at right angles to the base meeting the opposite side produced; then will the part produced, the perpendicular, and the remaining side, form an equilateral triangle.
56. In the figure Euc. I. 1, if the sides CA, CB of the equilateral triangle ABC be produced to meet the circles in F, G, respectively, and if C'' be the point in which the circles cut one another on the
other side of AB: prove the points F, C', G to be in the same straight line; and the figure CFG to be an equilateral triangle.
57. ABC is a triangle and the exterior angles at B and C are bisected by lines BD, CD respectively, meeting in D: shew that the angle BDC and half the angle BAC make up a right angle.
58. If the exterior angle of a triangle be bisected, and the angles of the triangle made by the bisectors be bisected, and so on, the triangles so formed will tend to become eventually equilateral.
59. If in the three sides AB, BC, CA of an equilateral triangle ABC, distances AE, BF, CG be taken, each equal to a third of one of the sides, and the points E, F, G be respectively joined (1) with each other, (2) with the opposite angles: shew that the two triangles so formed, are equilateral triangles.
60. Describe a right-angled triangle upon a given base, having given also the perpendicular from the right angle upon the hypotenuse.
61. Given one side of a right-angled triangle, and the difference between the hypotenuse and the sum of the other two sides, to construct the triangle.
62. Construct an isosceles right-angled triangle, having given (1) the sum of the hypotenuse and one side; (2) their difference.
63. Describe a right-angled triangle of which the hypotenuse and the difference between the other two sides are given.
64. Given the base of an isosceles triangle, and the sum or difference of a side and the perpendicular from the vertex on the base. Construct the triangle.
65. Make an isosceles triangle of given altitude whose sides shall pass through two given points and have its base on a given straight line.
66. Construct an equilateral triangle, having given the length of the perpendicular drawn from one of the angles on the opposite side.
67. Having given the straight lines which bisect the angles at the base of an equilateral triangle, determine a side of the triangle.
68. Having given two sides and an angle of a triangle, construct the triangle, distinguishing the different cases.
69. Having given the base of a triangle, the difference of the sides, and the difference of the angles at the base; to describe the triangle. 70. Given the perimeter and the angles of a triangle, to construct it.
71. Having given the base of a triangle, and half the sum and half the difference of the angles at the base; to construct the triangle.
72. Having given two lines, which are not parallel, and a point between them; describe a triangle having two of its angles in the respective lines, and the third at the given point; and such that the sides shall be equally inclined to the lines which they meet.
73. Construct a triangle, having given the three lines drawn from the angles to bisect the sides opposite.
74. Given one of the angles at the base of a triangle, the base itself, and the sum of the two remaining sides, to construct the triangle.
75. Given the base, an angle adjacent to the base, and the difference of the sides of a triangle, to construct it.
76. Given one angle, a side opposite to it, and the difference of the other two sides; to construct the triangle.
77. Given the base and the sum of the two other sides of a triangle, construct it so that the line which bisects the vertical angle shall be parallel to a given line.
78. From a given point without a given straight line, to draw a line making an angle with the given line equal to a given rectilineal angle. 79. Through a given point A, draw a straight line ABC meeting two given parallel straight lines in B and C, such that BC may be equal to a given straight line.
80. If the line joining two parallel lines be bisected, all the lines drawn through the point of bisection and terminated by the parallel lines are also bisected in that point.
81. Three given straight lines issue from a point: draw another straight line cutting them so that the two segments of it intercepted between them may be equal to one another.
82. AB, AC are two straight lines, B and C given points in the same; BD is drawn perpendicular to AC, and DE perpendicular to AB; in like manner CF is drawn perpendicular to AB, and FG to AC. Shew that EG is parallel to BC.
83. ABC is a right-angled triangle, and the sides AC, AB are produced to D and F; bisect FBC and BCD by the lines BE, CE, and from E let fall the perpendiculars EF, ED. Prove (without assuming any properties of parallels) that ADEF is a square.
84. Two pairs of equal straight lines being given, shew how to construct with them the greatest parallelogram.
85. With two given lines as diagonals describe a parallelogram which shall have an angle equal to a given angle. Within what limits must the given angle lie?
86. Having given one of the diagonals of a parallelogram, the sum of the two adjacent sides and the angle between them, construct the parallelogram.
87. One of the diagonals of a parallelogram being given, and the angle which it makes with one of the sides, complete the parallelogram, so that the other diagonal may be parallel to a given line.
88. ABCD, ABCD are two parallelograms whose corresponding sides are equal, but the angle 4 is greater than the angle A, prove that the diameter AC is less than AC", but BD greater
89. If in the diagonal of a parallelogram any two points equidistant from its extremities be joined with the opposite angles, a figure will be formed which is also a parallelogram.
90. From each angle of a parallelogram a line is drawn making
the same angle towards the same parts with an adjacent side, taken always in the same order; shew that these lines form another parallelogram similar to the original one.
91. Along the sides of a parallelogram taken in order, measure AA' = BB' = CC DD': the figure A'B'C'D' will be a parallelogram.
92. On the sides AB, BC, CD, DA, of a parallelogram, set off AE, BF, CG, DH, equal to each other, and join AF, BG, CH,DE: these lines form a parallelogram, and the difference of the angles AFB, BGC, equals the difference of any two proximate angles of the two parallelograms.
93. OB, OC are two straight lines at right angles to each other, through any point P any two straight lines are drawn intersecting OB, OC, in B, B, C, C', respectively. If D and D' be the middle points of BB and CC, shew that the angle BPD' is equal to the angle DOD.
94. ABCD is a parallelogram of which the angle C' is opposite to the angle A. If through A any straight line be drawn, then the distance of C is equal to the sum or difference of the distances of B and of D from that straight line, according as it lies without or within the parallelogram.
95. Upon stretching two chains AC, BD, across a field ABCD, I find that BD and AC make equal angles with DC, and that AC makes the same angle with AD that BD does with BC; hence prove that AB is parallel to CD.
96. To find a point in the side or side produced of any parallelogram, such that the angle it makes with the line joining the point and one extremity of the opposite side, may be bisected by the line joining it with the other extremity.
97. When the corner of the leaf of a book is turned down a second time, so that the lines of folding are parallel and equidistant, the space in the second fold is equal to three times that in the first.
98. If the points of bisection of the sides of a triangle be joined, the triangle so formed shall be one-fourth of the given triangle.
99. If in the triangle ABC, BC be bisected in D, AD joined and bisected in E, BE joined and bisected in F, and CF joined and bisected in G; then the triangle EFG will be equal to one-eighth of the triangle ABC.
100. Shew that the areas of the two equilateral triangles in Prob. 59, p. 78, are respectively, one-third and one-seventh of the area of the original triangle.
101. To describe a triangle equal to a given triangle, (1) when the base, (2) when the altitude of the required triangle is given.
102. To describe a triangle equal to the sum or difference of two given triangles.
103. Upon a given base describe an isosceles triangle equal to a given triangle.
104. Describe a right-angled triangle equal to a given triangle 105. To a given straight line apply a triangle which shall be equal
to a given parallelogram and have one of its angles equal to a given rectilineal angle.
106. Transform a given rectilineal figure into a triangle whose vertex shall be in a given angle of the figure, and whose base shall be in one of the sides.
107. Divide a triangle by two straight lines into three parts which when properly arranged shall form a parallelogram whose angles are of a given magnitude.
108. Shew that a scalene triangle cannot be divided into two parts which will coincide.
109. If two sides of a triangle be given, the triangle will be greatest when they contain a right angle.
110. Of all triangles having the same vertical angle, and whose bases pass through a given point, the least is that whose base is bisected in the given point.
111. Of all triangles having the same base and the same perimeter, that is the greatest which has the two undetermined sides equal.
112. Divide a triangle into three equal parts, (1) by lines drawn from a point in one of the sides: (2) by lines drawn from the angles to a point within the triangle: (3) by lines drawn from a given point within the triangle. In how many ways can the third case be done? 113. Divide an equilateral triangle into nine equal parts.
114. Bisect a parallelogram, (1) by a line drawn from a point in one of its sides: (2) by a line drawn from a given point within or without it: (3) by a line perpendicular to one of the sides: (4) by a line drawn parallel to a given line.
115. From a given point in one side produced of a parallelogram, draw a straight line which shall divide the parallelogram into two equal parts.
116. To trisect a parallelogram by lines drawn (1) from a given point in one of its sides, (2) from one of its angular points.
117. To describe a rhombus which shall be equal to any given quadrilateral figure.
118. Describe a parallelogram which shall be equal in area and perimeter to a given triangle.
119. Find a point in the diagonal of a square produced, from which if a straight line be drawn parallel to any side of the square, and meeting another side produced, it will form together with the produced diagonal and produced side, a triangle equal to the square.
120. If from any point within a parallelogram, straight lines be drawn to the angles, the parallelogram shall be divided into four triangles, of which each two opposite are together equal to one-half of the parallelogram.
121. If ABCD be a parallelogram, and E any point in the diagonal AC, or AC produced; shew that the triangles EBC, EDC, are equal, as also the triangles EBA and EBD.
122. ABCD is a parallelogram, draw DFG meeting BC in F,