sum of first n terms of an ap whose first term is 8 and the common difference is 20 is equal to the sum of first 20 terms of an ap whose first term is minus 30 and common difference is 8 find n
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Step-by-step explanation:
Considering the two sums as An and Sn'
Now Sn =Sn'
n/2(2a+(n-1)d) = n/2(2a'+(n-1)d')
n/2(16+(n-1)20). = 20/2(-60+19*8)
n/2(16+20n -20) = 10*92
16n + 20n^2 -20n = 10*92*2
20n^2 -4n = 1840
by factorisation methods and finding roots of the quadratic equation
n= 10
Note: always take integer and positive number for the value of n
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