Select the approximate values of x that are solutions to f(x) = 0, where f(x) = -5x2 + 4x + 7.

Question

 A. {-0.71,0.57}

B.{-5,4}

C. {-0.80,-1.40}

D.{-0.85,1.65}

Answer 1

f(x)=-5x²+4x+7

using the quadratic equation

[-4+√(16+140)]/(-10)

[-4+√(156)]/(-10)

[-4+√(4*39)]/(-10)

[-4+2√39]/(-10)

[-4+2(6.24499)]/(-10)

[-4+12.48998]/(-10)

(8.48998)/(-10)=-0.848998≈-0.85

(-16.48998)/(-10)=1.648998≈1.65

the answer is D)