f(-5)=2(-5)+1/3

Solution for f(-5)=2(-5)+1/3 equation:

f(-5)=2(-5)+1/3

We move all terms to the left:

f(-5)-(2(-5)+1/3)=0

We multiply parentheses

-5f-(2(-5)+1/3)=0

We multiply all the terms by the denominator


-5f*3)-(2(-5)+1=0

Wy multiply elements

-15f^2+1=0

a = -15; b = 0; c = +1;
Δ = b2-4ac
Δ = 02-4·(-15)·1
Δ = 60
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:

$\sqrt{\Delta}=\sqrt{60}=\sqrt{4*15}=\sqrt{4}*\sqrt{15}=2\sqrt{15}$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{15}}{2*-15}=\frac{0-2\sqrt{15}}{-30}
=-\frac{2\sqrt{15}}{-30}
=-\frac{\sqrt{15}}{-15}
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{15}}{2*-15}=\frac{0+2\sqrt{15}}{-30}
=\frac{2\sqrt{15}}{-30}
=\frac{\sqrt{15}}{-15}
$