P(3)=x^2+5x-7

Solution for P(3)=x^2+5x-7 equation:

(3)=P^2+5P-7

We move all terms to the left:

(3)-(P^2+5P-7)=0

We get rid of parentheses

-P^2-5P+7+3=0

We add all the numbers together, and all the variables

-1P^2-5P+10=0

a = -1; b = -5; c = +10;
Δ = b2-4ac
Δ = -52-4·(-1)·10
Δ = 65
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$P_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$P_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$P_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-\sqrt{65}}{2*-1}=\frac{5-\sqrt{65}}{-2}
$
$P_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+\sqrt{65}}{2*-1}=\frac{5+\sqrt{65}}{-2}
$