Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

And in the same way we may show that, if the corresponding terms of any number of proportions be multiplied together, the products will be proportional.

28. If three quantities are in continued proportion, the first has to the third the duplicate ratio of what it has to the second.

Let a, b, c be the given quantities in continued proportion; then

6

a

[ocr errors][ocr errors]

Hence,

a a

6 or Х

C

[ocr errors]

a a a?

Х

7

..a:c:: ? : 62. And, similarly, if a, b, c, d are four quantities in continued proportion, a : d::: 73, that is

The first has to the fourth the triplicate ratio of what it has to the second; and so on, for any number of quantities.

29. We shall now give one or two examples of problems in Proportion.

a3 + Ex. 1. If a : 6::c:d, prove that

73 M
a с
Let
7

da.
= 8; .'. a =
d

bx, and c =
as + c3
Hence,

(bx) + (dx)

73 + 2 (a + c)

(6x + dx) a3 + c3 nando, 63 + ď

Jac + sbd Ex. 2. If a : 6 :: :d, prove that

Jac - Vod

[ocr errors]
[ocr errors]

+

(6 + dya, then, alter

3

a + c

+

a + 6

a

[merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]

Or, it may

be worked thus

a

we have

[ocr errors]

sac

Or,

[ocr errors]

Х

[ocr errors]
[ocr errors]

x

Since d'

6

a

or 6

7 b Vid Hence, by Art. 26—

Jac + sod 6

Nod Ex. 3. If a :b :: c:d :: e:f, show that

ma" + nca + per 6 mb" + nd" + pf"

a + 6

a

Jac

a

[ocr errors]

a

C

[ocr errors]

= X.....

= "

[ocr errors][merged small]

Let

(1). b d

am

em

bi dr fr Hence, a" b*x*, may

mbaca C

nch ndc" and ... by addition, e" = f(z", : pe" pfc

ma" + nc+ pen (mb" + nd" + pfr)ą".
ma" + nom + pe" ma+ nc + per
Oc”, or

= 2... (2). mba

nd" + pfa mb" + nd" + pf .. Equating (1) and (2), we have (ma" + noh + per

Q.E.D. ū mb+ nd" + pf".

[blocks in formation]

1. Compare the ratios a + b:a b, and a + 62: a? 62. 2. Which is the greater of the ratios a + b : 2 a, and 26:a + 6?

3. What quantity must be subtracted from the consequent of the ratio a : b in order to make it equal to the ratio c:d?

4. Compound the ratios 1 - 2 : 1 + y, - wy? :1 + 20°, and 1:3 2cm.

5. There are two numbers in the ratio of 6 : 7, but if 10 be added to each they are in the ratio of 8 : 9. Find the numbers.

6 6. In what cases is a +

<5?

> or < WC

a

y + z

[ocr errors]

b + c

[ocr errors]

a

[ocr errors]

a

[ocr errors]

e

6 7. If

show that a + b + c = 0. y

ac' 8. Find the value of x when the ratio x + 2 a : x + 2 6 is the duplicate ratio of 2 x + a + c:22 + b + c.

9. Find x when the ratio x 6 : x + 2 a 6 is the triplicate ratio of a -a:* + a

b. 8C + y

+ 10. If

show that each of the frac

C + a' 2 + y + x

tions is equal to

and that a + b + c

6

la + mc + nc 11. If ł I

16 + md + nfi hence, show that

6
2 % + 2 x

Y
2 x + 2 y

2 y + 2x - od

y when 2 a + 2 6 2 b + 2 c

2 c + 2 a 6 12. If a :b :: c:d, then

a + b :c + d :: Va2 + ab + 62 : Vo? + cd. + d. 13. Find a fourth proportional to the quantities—

2 + 1 2 + x + 1 2 + 1
l'act
2 + 1 2013

1 14. Find c in terms of a and 6 when

(1.) a :a::a 6:6
(2.) a : 6:: a 6:6
(3.) a:0::a 6 6

a

с

[ocr errors]

C.

[ocr errors]

:

C.

15. If a, b, c are in continued proportion, show that a + 6

6, bc are also in continued proportion. b + c 16. If a :b::c:d, then

Vaan. + 62n : Voan + dân :: (a - b)" : (c d)". 17. From a vessel containing a cubic inches of hydrogen gas, b cubic inches are withdrawn, the vessel being filled up with oxygen at the same pressure.

Show that if this operation be repeated n times successively, the quantity of hydro

(a - b)" gen remaining in the vessel is cubic inches, when reduced to the original pressure.

18. If, in Ex. 34, page 225, (az, Ain, az), (61, 62, 63), and (C1, C2, C3) are corresponding terms respectively, show that abgbg (cz - Cz) + agbab (CG) + agbiba (a - C) = 0.

an

SECTION III.

PLANE TRIGONOMETRY.

CHAPTER I.

MODES OF MEASURING ANGLES BY DEGREES AND GRADES.

1. We are able to determine geometrically a right angle, and it might therefore be taken as the unit of angular measurement Practically, however, it is too large, and so we take a determinate part of a right angle as a standard.

In England we divide a right angle into 90 equal parts, called degrees, and we further subdivide a degree into 60 equal parts, called minutes, and again a minute into 60 equal parts, called seconds. This is the English or sexagesimal method.

In France the right angle is divided into 100 equal parts, called grades, a grade into a hundred equal parts, called minutes, and a minute into 100 equal parts, called seconds. This is the French or centesimal method, and its advantages are those of the metric system generally.

The symbols , \, ', are used to express English degrees, minutes, seconds respectively, and the symbols", ", to express French grades, minutes, seconds respectively.

Conversion of English and French Units. 2. Let D = the number of degrees in an angle, and G the number of grades in the same angle ;

D then expresses the angle in terms of a right angle; 90

G and so also does

« ΠροηγούμενηΣυνέχεια »