How do you factor the trinomial #x^2-4x-21#?

1 Answer
Nghi N.
Dec 4, 2015

Factor: #y = x^2 - 4x - 21#

Explanation:

#y = x^2 - 4x - 21#.
Find 2 numbers knowing sum (b = -4) and product (c = -21). The 2 numbers have opposite signs. Factor pairs of (-21) --> (-3, 7). This sum is 4 = -b. Then the opposite sum gives the 2 numbers : 3 and -7.
Factored form y = (x + 3)(x - 7)

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