(3a+b)² = (3a)^2 +2*3*a*b + b^2 = 9a^2 +6ab + b^2
(7v-u)² = (7v)^2 - 2*7v*u + u^2 = 49v^2 -14uv + u^2
12fg+(2f-3g)² = 12fg + (2f)^2 - 2*2f*3g + (3g)^2 = 12fg +4f^2 -12fg + 9g^2 = 4f^2 + 9g^2
25x²-(5x-1)² = 25
x²-((5x)² -2*5x*1+1²)= 25x²
- (25x² -10x +1)=25x² -25x² +10x-1 = 10x-1
-2·(5a-3)² = -2((5a)^2-2*3*5a+3^2)=-2*(25a^2-30a+9)=-50a^2+60a-18