Упростить выражения:

42ab - (3a+7b) ²=?

(x+7y) ²-14xy=?

25t² - (2z+5t) ²=?

(t-4) ² - (4-t) (t+4) = ?

(3t-5) ²-25=?

42ab - (9a^2 + 2*3*7*ab + 49b^2) = 42ab - 9a^2 - 42ab - 49b^2 = - (9a^2 + 49b^2)

x^2 + 14xy + 49y^2 - 14xy = x^2 + 49y^2

25t^2 - (4z^2 + 20tz + 25t^2) = 25t^2 - 4z^2 - 20tz - 25t^2 = - 4z^2 - 20tz = - 4z (z + 5t)

t^2 - 8t + 16 - (16 + t^2) = t^2 - 8t + 16 - 16 - t^2 = - 8t

9t^2 - 30t + 25 - 25 = 9t^2 - 30t = t (9t - 30)