Hint - Multiply the L . H . S by " ( 1 - t ) " , and remember that : -
1 - t n1 - t = 1 + t + t 2 . . . . . . . . + t n - 1 .
Hint - Multiply the L . H . S by " ( 1 - t ) " , and remember that : -
1 - t n1 - t = 1 + t + t 2 . . . . . . . . + t n - 1 .