1.

If the end term of an ap is given by (-4n+15)find the sum of first 20 terms of this AP. ​

Answer»

solution :-. GIVEN Tn = (-4n+15)

T1 = -4*1 + 15 = 11 , T1 = a = first term .

T2 = -4*2 +15 = 7

Common difference'd' = 7-11 = -4

S20 = n/2 {(2A+(n-1)d}

S20 = 20/2(2* 11 + (20-1)-4}

S20 = 10 (22 -76)

S20 = 10(-54)

S20 = -540 Answer .

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