The sum up to n terms of an A. P. is 48, first term is 20 and common difference is -4 . find the number of terms.
Answers
Answered by
1
48=20+(n-1)-4
48-20=(n-1)-4
28/-4=(n-1)
-7+1=n
-6=n
Answered by
1
As we know,
Sn=n/2[2a+(n-1)*d]
Here, a=20, d=-4 ,Sn=48
Therefore,
48=n/2[44-4n]
48=n[22-2n]
2n^2 - 22n +48=0
Now, solve this quadratic...,
Whatever will be the value of n... Will be the required number of terms.....
Hope it helps you.....
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