Find the zeros of f.

Question

f(x) = 2x2 + x − 21

smaller value = ___
larger value = ___

Answer 1

F(x) = 2x^2 + x - 21
Y = 2x^2 + x + 1 = 0
A*C Method:
A*C = 2 * (-21 = -42 = -3*14 = -6*7
Choose the pair of factors whose sum = B
-6+7 = 1 = B.
2x^2 + (-6x+7x) - 21 = 0
(2x^2-6x) + (7x-21) = 0
Factor each binomial:
2x(x-3) + 7(x-3) = 0
Factor out (x-3):
(x-3)(2x+7) = 0

x-3 = 0
X = 3.

2x+7 = 0
2x = -7
X = -7/2 = -3.5

Solution set: X = -7/2, and 3.

Note: You may also use the Quadratic Formula.