7. Add 4ax 90, and √x + 40 12 8. Add 2a2 6x2 together. Ans. 7ax +8x2 + 7xy. 3ab +263 3a2, 363 2a2 + a3 — 5c3, 4c3 2b35ab + 100, and 20ab + 16a2 80 together. c3 +20 - bc. be ) and + 8a b d b α and 4a2 9bc — 10e2 + 21 together. Ans. bc 6a2 9e2 + 16. SUBTRACTION. SUBTRACTION is the taking of one quantity from another or the method of finding the difference between any two quantities of the same kind; which is performed as follows: * RULE.-Change all the signs (+ and -) of the lower line, or quantities that are to be subtracted, into the contrary signs, or rather conceive them to be so changed, and then collect the terms together, as in the several cases of addition. * This rule being the reverse of addition, the method of operation must be so likewise. It depends upon this principle, that to subtract an affirmative quantity from an affirmative, is the same as to add a negative quantity to an affirmative. Thus, according to Laplace, we can write transformation (1), must be ab in the first case, and a+b in the second. Also, if from ac we take away +b, orb, the remainder, from (2), will be a-c-b, or a-cb.-ED. -8x3y-8a+ 76 ax-2xy +5xy2x2+8x+2√x-4y √ax-2x3y+5xy2 EXAMPLES FOR PRACTICE. 2 1. Find the difference of (a + b) and 1⁄2 (a - b). Ans. b. 2. From 3x 2a b+7, take 8 3. From 3a + b + c — 2d, take b 4. From 13x2 3b+ a + 4x. 2ax+962, take 5x2- 7ax b2. Ans. 8x2+5ax + 106a. 1 5. From 20ạx − 5 √ x + 3a, take 4ax + 5x2 √x a. Ans. 16ax 10 ✓ x + 4α. 6. From 5ab + 2b2 — c + bc — b, take b2 — Qab + bc. Ans. 7ab+b2 7. From ax3 bx2 + cx d, take bx2 + ex 2d. c — b 5c. Ans. ax3 2bx + (c − e) x + d. 8. From - 6a — 4b — 12c + 13x, take 4x 9a + 4b Ans. 3a +9x 86 - 7c. 9. From 6x3y — 3√(xy) — 6ay, take 3x2y + 3 (xy)3 — 4ay. Ans. 3x2y — 6 √(xy) — Qay. I 10. From the sum of 4ax- 150+ 4x3, 5x2 + 3ax +10x2, and 90 2ax 12 √(x); take the sum of 2ax — 80 + 7x3, 8ax — 70, and 30 — 4 √ (x) — 2x2 + 4a2x2. I Ans. 11ax+ 60 — x2 MULTIPLICATION. 4a2x2 MULTIPLICATION, or the finding of the product of two or more quantities, is performed in the same manner as in arithmetic; except that it is usual, in this case, to begin the operation at the lefthand, and to proceed towards the right, or contrary to the way of multiplying numbers. The rule is commonly divided into three cases; in each of which it is necessary to observe, that like signs, in multiplying, produce+, and unlike signs, -. It is likewise to be remarked, that powers, or roots of the same quantity, are multiplied together by adding their indices: thus, I a × a3, or a1 × a2 = a3; aa × a3 = a3; aa × a3 = a; and am X an = am+n. аг The multiplication of compound quantities, is also, sometimes, barely denoted by writing them down, with their proper signs, under a vinculum, without performing the whole operation, as 3ab (a — b), or 2a √ (a2 + b2). Which method is often preferable to that of executing the entire process, particularly when the product of two or more factors is to be divided by some other quantity, because, in this case, any quantity that is common to both the divisor and dividend, may be more readily suppressed; as will be evident from various instances in the following part of the work.* CASE I. When the factors are both simple quantities. RULE.-Multiply the coefficients of the two terms together, and to the product annex all the letters, or their powers, belonging to each, after the manner of a word; and the result, with the proper sign prefixed, will be the product required.† *The above rule for the signs may be proved thus: If B, b, be any two quantities, of which B is the greater, and B b is to be multiplied by a, it is plain that the product, in this case, must be less than ав, bеcause B -b is less than B; and, consequently, when each of the terms of the former are multiplied by a, as above, the result will be (B—b) × α = аB --- ab. For if it were aв+ab, the product would be greater than aв, which is absurd. Also, if в be greater than b, and a greater than a, and it is required to multiply B- -b by a the result will be (Bb)X(sa) — AB — аB — b▲ † ab. ав B For the product of B b by A is A (Bb), or AB- ·Ab, and that of B-b by b bya, which is to be taken from the former, is a (в - b) as has been already shown; whence в - b being less than в, it is evident that the part, which is to be taken away must be less than aв; and consequently since the first part of this product is aв, the second part must be ab; for if it were -ab, a greater part than aв would be to be taken from A (B --b), which is absurd. + When any number of quantities are to be multiplied together, it is the same thing in whatever order they are placed: thus, if ab is to be When one of the factors is a compound quantity. RULE.-Multiply every term of the compound factor, considered as a multiplicand, separately, by the multiplier, as in the former case; then these products, placed one after another with their proper signs, will be the whole product required. multiplied by, the product is either abc, acb, or bca, &c.; though it is usual, in this case, as well as in addition and subtraction, to put them according to their rank in the alphabet. It may here also be observed in conformity to the rule given above for the signs, that (+-a) ×(-+-6). or (——a) × (--b) =+ab; and ( + a) × ( —b), or ( − a) × (+ - ab. CASE III. When both the factors are compound quantities. RULE.-Multiply every term of the multiplicand separately, by each term of the multiplier, setting down the products one after another, with their proper signs; then add the several lines of products together, and their sum will be the whole product required. 1. Required the product of x2- xy + y2 and x+y. Ans. 3y3. 2. Required the product of x3 + x2y + xy2 + y3 and x 4. Required the product of 3x2 - 2xy +5, Ans. 3x+4x3y — 4x2y2 y. 4 Ans x - y1. and x2-xy -+ y2. xxy3 +ya. х 2 and x2+2xy — 3. 4x2 + 16xy - 15. 5. Required the product of 2a2 3ax 4x2 and 5a2 6ax 202. Ans. 10a1 27a3x + 34a2x2 —18ax3 6. Required the product of 53+ 4x2 + 3a2x + a3, and 3ax + a2. 3a3x2+a3. 7. Required the product of 33 + 2x2y2+ 3y3 and 2x3 2x2 3x2y2 +5y3. Ans. 10x5 4.4 7ax1 a2x3 5x5у2-6x11+21x3y3 + x2 + 15yo. 8. Required the product of a3 ax2 + bx c and x2 Ans. 6x6 +e. Ans. a 4 — dx ax2- dx2 + (b + ad + e) x3- (c+bd+ae) x2+(cd + eb) x-ce. |