Question

Factor 2x^2 - 11x - 21

A. (2x + 3)(x - 7)
B. (x + 3)(2x - 7)
C. (2x - 3)(x + 7)
D. (2x + 7)(x - 3)

Please explain how to do this, don't just give the answer. Thanks.

Answer 1

once my friend is avalable ill ask her to answer an exsplain this too you ok..=)

Answer 2

can i give you ans

Answer 3

ans is a

Answer 4

(ax+b)(cx+d) = acx^2 + (bc+ad)x + bd

that's the general rule.

your problem has -21 = bd, and all your choices have -21 when you multiply the, so that does not eliminate any.

your problem has 2x^2 and all your choices have ac=2, so that does not eliminate any of them, either

your problem has -11x, so (bc+ad) = -11, and we have to check to see which option has this
a. (2x+3)(x-7) a=2, b=3, c=1, d=-7 bc+ad= 3-14 = -11 bingo! just what we wanted. so @akshay1234 is right.

b. (x+3)(2x-7) a=1, b=3, c=2, d=-7, bc+ad = 6-7=-1 not -11

try c. and d. but they are not right, as a. is the correct answer.