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Feb/Mar 2019 p12 q6
893
The first and second terms of a geometric progression are p and 2p respectively, where p is a positive constant. The sum of the first n terms is greater than 1000p. Show that 2n > 1001.
Solution
\(The first term of the geometric progression is a = p and the common ratio is r = 2.\)
The sum of the first n terms of a geometric progression is given by:
\(S_n = \frac{a(r^n - 1)}{r - 1}\)
Substituting the values, we have:
\(S_n = \frac{p(2^n - 1)}{2 - 1} = p(2^n - 1)\)
We are given that:
\(p(2^n - 1) > 1000p\)
Dividing both sides by p (since p is positive), we get: