Chapter 4 - Quadratic Functions - 4.6 Solving Quadratic Equations by Using the Quadratic Formula - 4.6 Exercises - Page 372: 10

$x=\frac{40}{3}$ $x\approx-16$

$-3x^2-8x+1000=360$ $-3x^2-8x+1000-360+0$ $-3x^2-8x+640=0$ $3x^2+8x-640=0$ Comparing with quadratic equation $ax^2+bx+c=0$ $a=3,b=8,c=-640$ Putting in the formula $x=\frac{-b \pm \sqrt {b^2-4ac}}{2a}$ $x=\frac{-8 \pm \sqrt {8^2-4(3)(-640)}}{2(3)}$ $x=\frac{-8 \pm \sqrt { 7744}}{6}$ $x=\frac{-8 \pm 88}{6}$ $x=\frac{40}{3}$,$x\approx-16$