Question 214675
Starting with:
-2x^2+8x+20=0
Multiply both sides by -1:
2x^2-8x-20=0
Divide both sides by 2:
x^2-4x-10=0
Always try to factor to find the answer first.  In this case, it can't be factored so you must resort to the quadratic equation.  Doing so yields:
x = {5.7412, -1.742}
.
Details of quadratic:
*[invoke quadratic "x", 1, -4, -10 ]