25x^2-90=-81

Solution for 25x^2-90=-81 equation:

25x^2-90=-81

We move all terms to the left:

25x^2-90-(-81)=0

We add all the numbers together, and all the variables

25x^2-9=0

a = 25; b = 0; c = -9;
Δ = b2-4ac
Δ = 02-4·25·(-9)
Δ = 900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{900}=30$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-30}{2*25}=\frac{-30}{50}
=-3/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+30}{2*25}=\frac{30}{50}
=3/5
$