folosim formula (a+b)²=a²+2ab+b²²
(2√5+√3)²=2²√5²+2·2√5·3+√3²=20+12√5+3=23+12√5
(1/2+2x)²=1/4+2·1/2·2x+x²=x²+2x+1/4=4x²+8x+1
(1/3x+3y)²=1/9x²+2·1/3x·3y+9y²=1/9x²+2y/x+9y²=1+18xy+81x²y²
(3/4x+4/3y)²=9/16x²+2·3/4x·4/3y+16/9y²=9/16x²+2/xy+16/9y²=81y²+288xy+256x²
