quadratic equations

Question

Select the approximate values of x that are solutions to f(x) = 0, where
f(x) = -7x2 + 7x + 6.
 

The four options are:

{–0.55, 1.55}

{-7, 7}

{–1.00, –0.86}

{–1.17, 1.17}

Answer 1

-7x² + 7x + 6 = 0

 

By the quadratic formula,

 

x = (-7 ± √[(7)² - 4(-7)(6)]/(2(-7))

 

x = (-7 ± √[49 + 168]/(-14)

 

x = (-7 ± √217)/(-14)

 

x ≈ -0.55, 1.55