How do you factor 3x^2 + 5x - 283x2+5x−28?

2 Answers
ali ergin
Apr 21, 2016

3x^2+5x-28=(3x-7)(x+4)3x2+5x−28=(3x−7)(x+4)

Explanation:

3x^2+5x-28=(3x-7)(x+4)3x2+5x−28=(3x−7)(x+4)

Nghi N.
Apr 21, 2016

(3x - 7)(x + 4)

Explanation:

Use the new AC method to factor trinomials (Socratic Search)
y = 3x^2 + 5x - 28 =y=3x2+5x−28= 3(x + p)(x + q)
Converted trinomial y' = x^2 + 5x - 84 = (x + p')(x + q')
p' and q' have opposite signs, because ac < 0.
Factor pairs of (ac = -84) -->...(-4, 21)(-7, 12). This sum is 5 = b. Then, p' = -7 and q' = 12.
Back to y, p = (p')/a = -7/3 and q = (q')/a = 12/3 = 4.
Factored form:
y = 3(x - 7/3)(x + 4) = (3x - 7)(x + 4)

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