There is no number of which we cannot find any power exctly ; but there are many numbers, of which the exact roots can never be obtained. Yet, by the help of decimals, we can obtain these roots to any necessary degree of exactness.

Those roots which cannot be exactly obtained, are called surd rools ; and those which can be found exactly, are called rational roots.

Roots are sometimes denoted by writing this character v before the power, with the index of the power over it ; thus the cube root of 64 is expressed ✓ 64, and the square root of 64 is expressed ✓ 64, the index 2 being omitted when the square root is required

EXTRACTION OF THE SQUARE ROOT.

The EXTRACTION OF THE SQUARE Root is the method of finding a number, which, being multiplied by itself, shall produce the iven number.

RULE.

1. Distinguish the given number into periods of two figures each, by putting a point over the place of units, another over the place of bundreds, and so on, which points show the number of figures the root will consist of.

2. Find the greatest square number in the first, or left hand period ; place the root of it at the right hand of the given number, after the manuer of a quotient in division,) for the first figure of the root, and the square number under the period, then subtract it therefrom, and to the remainder bring down the next period for a dividend.

3. Place double of the root, already found, on the left hand of the dividend for a divisor.

4. Seek how often the divisor is contained in the dividend, (except the right hand figure,) and place the answer in the root for the second figure of it, and likewise on the right had of the divisor ; multiply the divisor with the figure last annexed by the figure last placed in the root, and subtract the product from the dividend : to the remainder join the next period for a new dividend.

5. Double the figures already found in the root, for a new divisor, (or bring down your last divisor for a new one, doubling the right hand figure of it,) and from these, find the next figure of the root as last directed, and continue the operation in the same manner, till you have brought down all the periods.*

* The rule for the extraction of the square root may be illustrated by attending to the process by which any number is raised to the square. The several products of the multiplication are to be kept separate, as in the proof of the rule for multiplication of sim. ple numbers. Let 37 be the number to be raised to the square. 37X37=1369

237X37 37

37

49—72

4972
21 53X77

210=30X71
21 3X7S
=2X3X7

-2X30X7

210–30X7 9-32

900302

(37

(30+7=37 2X3)42 2X3X7

4972 Now it is evident that 9, in tne place of hundredths, is the greatest square in this product; put its root, 3, in the quotient, and 900 is taken from the product. The next products are 21+21=2X3X7, for a dividend. Double the root alıeady found, and it is 2X3, for a divisor, which gives 7 for the quotient, which annexed to the divisor, and the whole then multiplied by it, gives 2X3X7142)+7X7(=49) which, placed in their proper places, completely exhausts the remainder of the square. The same may be shown in any other case, and the rule becomes obvious.

Perhaps the following method may be considered more simple and plain. Let 37=30+7, be multiplied as in the demonstration of multiplication of simple numbers, and tbe products kept separate.

30+7
30-47
900+30X7

30X 77-49
900+2X30X7+49=1316, the sum and square.
900

30+7
2X30+7x7)2X30X3749

2X30X7+49

NOTE 1. If when the given power is pointed off as the power requires, the left hand period should be deficient, it must nevertheless stand as the first period.

2. If there be decimals in the given number, it must be pointed both ways from the place of upits: If when there are integers, the first period in the decimals be deficient, it may be completed hy anpexing so many ciphers as the power requires : And the root must be made to consist of so many whole numbers and decimals as there are periods belonging to each; and wheo the periods belonging to the given number are exhausted, the operation may be continued at pleasure by annexing ciphers.

EXAMPLES

1. Required the square root of 729 ?

PROOF.

a

729(27 the root. The given pumber being distinguished in4

to periods, we seek the greatest square pum

ber in the left hand period (7) which is 4, 47)329

of which the root (2) being placed to the 329

right hand of the given number, after the

mapper of a quotient, and the square number 000

(4) subtracted from the period (7) to the remainder (3) we bring down the next period

(29) making for a dividend, 329. Then the 27

double of the root (4) being placed to the left hand for a divisor, we say how often 4 in 32?

(excepting 9 the right hand figure) the answer 189

is 7, which we place in the root for the se54

cond figure of it, and also to the right hand

of the divisor; then multiplying the divisor 729

thus increased by the figure (7) last obtained in the root, we place the product underneath the dividend, and subtract it therefrom, and the work is done.

27

DEMONSTRATION OF THE REASON AND NATURE OF THE RULE.

a

The superficial content of any thing, that is to say, the number of square feet, inches, &c. in the surface of a field, a floor, &c. is found by multiplying the length into the breadth. Thus, if a piece of land be 10 rods in length, and 10 in width, it is a square, and the measure of ope of its sides is the root, of which the superficial content of the piece of land is the 2d power. Or, supposing you bave a piece of cloth 1 yard wide, and 225 yards in length, and you wish to know how many square yards it will cover, you must so arrange the parts of the whole that they may be in a square form.

Now, suppose you have 144 square pieces of wood, and wish to know how many pieces would be on a side, were the whole arranged into a square form. To determine this, you must extract the square root 144; the first step of which is to point off the number into periods of two figures each. This shows how many figures the root will consist of, and is done on this principle, that the product of any two numbers can have, at most, but as many places of figures, as are in both the factors, and at least but one less.

144(1

44

The left hand period being 1,

the square of it will be 1, and 1

likewise the root will be 1. But as we have nothing to do at present with the right hand period,

we will omit it, and consider only Fig. 1.

the left hand period, which being in the place of bundreds, must be called 100; hence the operation, at present, will be to find the square root of 100.

The root of 1, is 1, but as there are two periods in 100, there will be iww fig. ures in its root, and as the figure already obtained in the root is equal to its period, there is nothing remaining for the next period; and as the next period consists wbolly of ciphers, the next figure of the root will be a cipher, so that the root of 100 is 10. By this process we have

disposed of 100 of the pieces into the form represented by Fig. 1, viz. 10 pieces on a side.

The reason for placing the square number underneath the period, and subtracting it from the period, as directed in the rule, is as fol. lows. When we have obtained the root of the left hand period, we have disposed of as many pieces as the greatest square of the left hand period represents, and by subtracting the square of the runt from its period, we make it smaller by as many as the square of the root represents; thus in the example given, 1 in the quotient represents 10, the square of which is 100, which 1, under the left hand period, represents. This, subtracted from the left hand period, leaves 44 ; so that 100 pieces have been disposed of as represented by Fig. 1, and 44 pieces are now to be added to it, in such manner that the square form will be preserved. To do this, the rule directs to “pluce the double of the root already found on the left hand of the dividend for a divisor.