(2a+7b)в квадрате (а+3)(а-3) (8х+5у)(5у-8х)

(2a+7b)^2=4a^2+28ab+49b^2

(a+3)(a-3)=a^2-3a+3a-9=a^2-9

(8x+5y)(5y-8x)=40xy-64x^2+25y^2-40xy=25y^2-64x^2

(2a+7b)² = 4a²+28ab+49b²

(а+3)(а-3) = a²-9

(8х+5у)(5у-8х) = 25y² - 64x²