90=-4.9x^2+45x+87.2

Solution for 90=-4.9x^2+45x+87.2 equation:

90=-4.9x^2+45x+87.2

We move all terms to the left:

90-(-4.9x^2+45x+87.2)=0

We get rid of parentheses

4.9x^2-45x-87.2+90=0

We add all the numbers together, and all the variables

4.9x^2-45x+2.8=0

a = 4.9; b = -45; c = +2.8;
Δ = b2-4ac
Δ = -452-4·4.9·2.8
Δ = 1970.12
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-45)-\sqrt{1970.12}}{2*4.9}=\frac{45-\sqrt{1970.12}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-45)+\sqrt{1970.12}}{2*4.9}=\frac{45+\sqrt{1970.12}}{9.8}
$