Select the approximate values of x that are solutions to f(x) = 0, where f(x) = -9x2 + 4x + 7.

Question

Select the approximate values of x that are solutions to f(x) = 0, where
f(x) = -9x2 + 4x + 7.

Answer 1

f(x) = -9x^2 + 4x + 7 = 0

 

x = (-b ± √(b^2-4ac))/(2a)

 

x = (-(4) ± √((4)^2-4(-9)(7)))/(2(-9))

 

x = (4 ± 2√(4+9(7)))/(2(9))

 

x = (2 ± √(67))/9

 

check:

 

-9((2 ± √(67))/9)^2 + 4((2 ± √(67))/9) + 7 =? 0

-4/9 ± (-4)√(67)/9 - 67/9 + 8/9 ± 4√(67)/9 + 7 =? 0

-4/9 - 67/9 + 8/9 + 63/9 ± (-4)√(67)/9 ± 4√(67)/9 =? 0

-71/9 + 71/9 ± (-4)√(67)/9 ± 4√(67)/9 = 0 √