f(2)=3*(2)+5

Solution for f(2)=3*(2)+5 equation:

f(2)=3(2)+5

We move all terms to the left:

f(2)-(3(2)+5)=0

We add all the numbers together, and all the variables

f2-37=0

We add all the numbers together, and all the variables

f^2-37=0

a = 1; b = 0; c = -37;
Δ = b2-4ac
Δ = 02-4·1·(-37)
Δ = 148
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{148}=\sqrt{4*37}=\sqrt{4}*\sqrt{37}=2\sqrt{37}$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{37}}{2*1}=\frac{0-2\sqrt{37}}{2}
=-\frac{2\sqrt{37}}{2}
=-\sqrt{37}
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{37}}{2*1}=\frac{0+2\sqrt{37}}{2}
=\frac{2\sqrt{37}}{2}
=\sqrt{37}
$