3(2x+5y)²-5x-3y)²

3(2x+5y)²-(5x-3y)²= =3(4x²+20xy+25y²)-(25x²-30xy+9y²)= = 12x²+60xy+75y²-25x²+30xy-9y²= =-13x²+90xy+66y²

3(2x+5y)²-(5x-3y)² =3(4x²+2*2x*5y+25y²)-(25x²-2*5x*-3y+9y²) =3(4x²+20xy+25y²)-(25x²-30xy+9y²) =12x²+60xy+75y²-25x²+30xy-9y² =-13x²+90xy+66y² na pewno jest dobrze ;)

3(2x+5y)²-5(x-3y)²=3(4x²+20xy+25y²)-5(x²-6xy+9y²)=12x²+60xy+75y²-5x²+30xy-45y²=7x²+90xy+30y²