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Pankaj Mahendru Grade:
        if sum of four terms of GP is 60 and am between first and last term is 18. then find a and r.
6 years ago

Answers : (2)

jagdish singh singh
168 Points
										

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6 years ago
Uttam Gulshan
31 Points
										

See this solution and answer me if you are satisfied.


Let the numbers be a , ar , ar^2 , ar^3 .


Now, sum=60.


=> a + ar + ar^2 +ar^3 =60.    ...........(i).


Also, a + ar^3 = 18*2 = 36.      ...........(ii).


=> a ( r + r^3 ) = 36.


=> a = 36 / ( r + r^3).


Now putting this in eq.(i) , we get 24(r^3) - 36(r^2) - 36r +24 = 0.


=> r = 1/2 , -1 , 2.


r=1 doesn't satisfy the condition.


So r=2 or r=1/2


When r=2 , a=4 , and when r=1/2 , a=32. Hence, solved.

6 years ago
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