[فداك يارسول الله]

((1+ت)^2)^2ن - ( (1-ت)^2 )^2ن

( 1 +2ت -1 )^2ن - (1 -2ت -1 )^2ن

(2 ت )^2ن - (-2 ت )^2ن

(-4 )^ن - ( -4 ) ^2

= صفر