a)(a-b)²=a²+b²-2ab
(x-4)²=x²+4²-2*x*4=x²+16-8x=x²-8x+16
b)(a+b)²=a²+b²+2ab
(2x+1)²=(2x)²+1²+2*2x*1=4x²+4x+1
c)(a-b)(a+b)=a²-b²
(x+5)(x-5)=x²-5²=x²-25
d)(a+b+c)²=a²+b²+c²+2ab+2ac+2bc
(x+2+√2)²=x²+2²+√2²+2*x*2+2*x*√2+2*2*√2=x²+4+2+4x+2√2x+4√2=x²+2(2x+√2x)+2(3+2√2)
