X^2-15=3,5x

Solution for X^2-15=3,5x equation:

X^2-15=3.5X

We move all terms to the left:

X^2-15-(3.5X)=0

We add all the numbers together, and all the variables

X^2-(+3.5X)-15=0

We get rid of parentheses

X^2-3.5X-15=0

a = 1; b = -3.5; c = -15;
Δ = b2-4ac
Δ = -3.52-4·1·(-15)
Δ = 72.25
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{-(-3.5)-\sqrt{72.25}}{2*1}=\frac{3.5-\sqrt{72.25}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3.5)+\sqrt{72.25}}{2*1}=\frac{3.5+\sqrt{72.25}}{2}
$