Please help!! Select the approximate values of x that are solutions to f(x) =0, where f(x) = -9x^2 +4x+7

Question

a) {-1.29,0.57}

b) {-9,4}

c) {-0.44,-0.78}

d) {-0.69,1.13}

 

Answer 1

f(x) = 0

 

-9x² + 4x + 7 = 0

 

We use he quadratic formula:

 

x = (-b ± √(b² - 4ac))/(2a)

 

where  a=-9  ,   b=4   ,    c=7

 

x = [-4 ± √(4² - 4(-9)(7))] / [2(-9)]

 

x = (-4 ± √(16 + 252))/(-18)

 

x = (-4 ± 16.37)/(-18)

 

x₁ = -0.687

x₂ = 1.131

 

Your answer is (d).