This question has been making me mad all day! It's in a advanced maths text book and my teacher asked us to do it for homework.
Here's the question:
How many terms of the sequence 4, 3, 2.25, ... can you add before the sum exceeds 12?
Here's my working out:
The answer I got is n=-2 and it's incorrect. I checked the answer for this question at back of text book and it was n=4. I tried and tried but still got n=-2. Please help!
Answer
Hint. From the line $$ 1-\left(\frac34 \right)^n>\frac34 $$ you get $$ \left(\frac34 \right)^n<\frac14 $$ giving $$ n>\frac{\log(1/4)}{\log(3/4)}=4.8\ldots $$ that is $$n=5.$$
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