2)52²-25²/79²-51²
3)181²-61²/319²-77²
4)200²-380²/420²-160²​

2) (52²-25²)/(79²-51²) = (52-25)(52+25) / (79-51)(79+51) = (27*77) / (28*130) = (27*11) / (4*130) = 297/520

3)(181²-61²)/(319²-77²) = (181-61)(181+61) / (319-77)(319+77) = (120*242) / (242*396) = 30/99 = 10/33

4)(200²-380²)/(420²-160²​) = (200-380)(200+380) / (420-160)(420+160) = (-180*580)/(260*580) = -9/13