f(2)=f(1)+2

Solution for f(2)=f(1)+2 equation:

f(2)=f(1)+2

We move all terms to the left:

f(2)-(f(1)+2)=0

We add all the numbers together, and all the variables

f2-(f+2)=0

We add all the numbers together, and all the variables

f^2-(f+2)=0

We get rid of parentheses

f^2-f-2=0

We add all the numbers together, and all the variables

f^2-1f-2=0

a = 1; b = -1; c = -2;
Δ = b2-4ac
Δ = -12-4·1·(-2)
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-3}{2*1}=\frac{-2}{2}
=-1
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+3}{2*1}=\frac{4}{2}
=2
$