f(2)=-2f(1)=1

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

f(2)=-2f(1)=1

We move all terms to the left:

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

We add all the numbers together, and all the variables

f2-(-2f)=0

We add all the numbers together, and all the variables

f^2-(-2f)=0

We get rid of parentheses

f^2+2f=0

a = 1; b = 2; c = 0;
Δ = b2-4ac
Δ = 22-4·1·0
Δ = 4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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