In a GP 72+144

In a GP the sum of the 2nd term and fifth term is 72 and the sum of the 3rd term and 6th term is 144. find the common ratio, find the first term, find the sum of the first six terms

Correct answer:

q =  2
a1 =  4
s6 =  252

Step-by-step explanation:

s25=72 s36=144  a1 (q+q4)=s25 a1 (q2+q5)=a1 q(q+q4)=s36  q s25=s36  q=s36/s25=144/72=2
a1=q+q4s25=2+2472=4
s6=a1 (1+q+q2+q3+q4+q5)=4 (1+2+22+23+24+25)=252



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