Asked by akorede

if the 7th term of an a.p is twice the third term and the sum of the first four terms is-16 and the last and the last term is 72, find the number of the terms
Answered by akorede
show me the answer
Answered by Leo Galleguillos
Let a<sub>n</sub> be the n<sup>th</sup> term of arithmetic progression a. Can you then start to write out your ap using symbols?
Answered by oobleck
not so.
I'll show you how to find the answer.
Using the formula for the nth term of an AP, you know that
a+6d = 2(a+2d)
4/2 (2a+3d) = 16
Now you can find a and d, so you just need to know how many terms there are.
If there are k terms, then
a+(k-1)d = 72
so using a and d found in part 1, solve for k.
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