How do you solve 4X squared plus 8X minus 20 equals 0?

Answer 1

-- Although not required, you can make it slightly easier on yourself
if you first divide each side of the equation by 4.

-- Either way, you're left with a quadratic equation that isn't easily
factorable by inspection, so you're forced to use the quadratic formula
which you learned and then forgot.

-- The quadratic formula says that when you have the quadratic equation
[ Ax2 + Bx + C = 0 ],
which is exactly what you have, the two solutions are
x = 1/2A [ -B + sqrt(B2-4AC) ]
and
x = 1/2A [ -B - sqrt(B2-4AC) ].
This is the perfect time to use the quadratic formula,
and that's exactly how you solve your equation.