15 ! ) г) (2x+3y)^2-5xy д) 60ab-(4a+7b)^2 -2t^2)^2-20s^2t^2 д)(2a+b)(2a-b) е) (x-3y)(x+3y) ж)(7z+3t)(7z-3t) заранее ! )

Г)4x^2+12xy+9y^2-5xy=4x^2+7xy+9y^2. d) 60ab-16a^2-56ab-49b^2=4ab-16a^2-49b^2. E)-(25s^4-20s^2t^2+4t^4)-20s^2t^2=-25s^4-4t^4. D) 4a^2-b^2. E)x^2-9y^2. G) 49z^2-9t^2.