To prove that:To prove it using induction: 1) Confirm it is true for n = 1 It is true since 1/2 = 1/2^1 2) Assume it is true for some value of n = k i.e. ----> eqn (1) 3) Now prove it is true for n = k+1 i.e. the sum up to (k+1) terms = 1 - 1/2^(k+1) Proof: For n = k+1, the expression of the sum is: = ---> from eqn(1) = ---> taking common denominator 2^(k+1) = ---> simplifying the numerator = Proved! 4) So we have proved that if the formula is true for n=k, it is true for n=k+1. Since it is true for n=1, it is proved by mathematical induction, that it is true for all n. Hope you got it :)