Question

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

Answer 1

$-7x^2 +4x+9=0\\ \Delta=4^2-4\cdot(-7)\cdot9=16+252=268\\ \sqrt{\Delta}=\sqrt{268}=2\sqrt{67}\\ x_1=\frac{-4-2\sqrt{67}}{2\cdot(-7)}=\frac{-4-2\sqrt{67}}{-14}=\frac{2+\sqrt{67}}{7}\approx1.46\\ x_2=\frac{-4+2\sqrt{67}}{2\cdot(-7)}=\frac{-4+2\sqrt{67}}{-14}=\frac{2-\sqrt{67}}{7}\approx-0.88$