III.Answer the following:35.Find the sum of first twenty terms of Arit

1.	III.Answer the following:35.Find the sum of first twenty terms of Arithmetic series2+7+ 12 +...using suitable formula.
Answer» Given series is in AP with first term a = 2, common difference d = 7 - 2 = 5 Sum of n terms of an AP isSn = n/2[2a + (n-1)d] Therefore,Sum of first twenty termsS20 = 20/2[22 + 195] = 10(4 + 95) = 10*99 = 990

III.Answer the following:35.Find the sum of first twenty terms of Arithmetic series2+7+ 12 +...using suitable formula.

Answer»

Given series is in AP with first term a = 2, common difference d = 7 - 2 = 5

Sum of n terms of an AP isSn = n/2[2a + (n-1)d]

Therefore,Sum of first twenty termsS20 = 20/2[2*2 + 19*5] = 10(4 + 95) = 10*99 = 990