Выполните умножение: (x-5)*(x+5)= (7c+3)*(7c-3)= (4x-9y)*(4x+9y) (-2b)*(+2b)=

№1

(x - 5) * (x + 5) = х * х + х * 5 - 5 * х - 5 * 5 = х^2 + 5x - 5x - 25 = x^2 - 25.

№2

(7c + 3) * (7c - 3) = 7c * 7c + 7c * (-3) + 3 * 7c + 3 * (-3) = 49c^2 - 21c + 21c - 9 = 49c^2 - 9.

№3

(4x - 9y) * (4x + 9y) * (-2b) * (+2b) = (4x * 4x + 4x * 9y - 9y * 4x - 9y * 9y) * (-2b) * (+2b) = (16x^2 + 36xy - 36xy - 81y^2) * (-2b) * (+2b) = (16x^2 - 81y^2) * (-2b) * (+2b) = (16x^2 - 81y^2) * (-4b^2) = 16x^2 * (-4b^2) - 81y^2 * (-4b^2) = -64x^2b^2 + 324y^2b^2.