a) aici se aplica formula (a-b)(a+b)= a²-b²
(x-2y)(x+2y) = x²-(2y)² = x²-4y²
b) 2(x+y-3) = 2x+2y-6
c) e o formula (a-b)² = a²-2ab+b²
(2x-1)³ = (2x-1)²(2x-1) = (2²-2*2x*(-1)+1²)(2x-1) = (4+4x+1)(2x-1)= (5+4x)(2x-1) = 5*2x-5*(-1)+4x*2x+4x*(-1) = 10x+5+8x²-4x = 8x²+6x+5
