=(D-64)2
We move all terms to the left:
-((D-64)2)=0
We calculate terms in parentheses: -((D-64)2), so:
(D-64)2
We multiply parentheses
2D-128
Back to the equation:
-(2D-128)
We get rid of parentheses
-2D+128=0
We move all terms containing D to the left, all other terms to the right
-2D=-128
D=-128/-2
D=+64
