Saturday, February 6, 2010

Use math induction to prove that each statement is true for every positive integer n?

1/2+1/4+1/8+...+1/2^n=1-1/2^nUse math induction to prove that each statement is true for every positive integer n?
prove it is true for 1


(1/2)^1 = 1/2


1-(1/2)^1 = 1/2


now assume it is true for some integer k


1/2 + ... 1/2 ^ k = 1- 1/2^ k


now prove it is true for (k+1)


S( k+1) = 1-(1/2)^k + 1/2^(k+1)


S(k+1) = 1-(1/2)^k+1/2 (1/2^k)


S(k+1)=1- 1/2 (1/2)^k


S(k+1)= 1- (1/2)^ (k+1)


since it is also true for (k+1) this integer must be true for all positive integer n





hope this helps Use math induction to prove that each statement is true for every positive integer n?
n=1: 1/2^1 = 1 - 1/2^1. True for n = 1.





Now we must show that ';true for n = k'; implies ';true for n = k+1';. We do this by assuming the premise, and then we must use that to prove the conclusion. So assume:


1/2 + 1/4 + ... + 1/2^k = 1 - 1/2^k





Then we substitute the right hand side into the expression for k+1:


1/2 + 1/4 + ... + 1/2^(k+1) = 1 - 1/2^k + 1/2^(k+1)





But 2^(k+1) can also be written as 2 * 2^k, right hand side becomes:


1 - (2 - 1) / (2 * 2^k) = 1 - 1/2^(k+1)





Putting it together:


1/2 + 1/4 + ... + 1/2^(k+1) = 1 - 1/2^(k+1)





Completing the proof by induction.

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