Find the sum of first 20 terms of an A.P. whose nth term is given by T

1.	Find the sum of first 20 terms of an A.P. whose nth term is given by Tn = (7 - 3n).(A) 382(B) -490(C) 420(D) -382
Answer» The correct option is: (B) -490 Explanation: We have, T_n = (7 -3n) First term, T₁ = (7 -3 x 1) = 4 Second term, T₂ = 7 - 3 x 2= 1 Third term, T₃ = 7 -3 x 3 = -2 .'. Series is 4, 1, - 2, .......... and common difference = -3 Sum of first 20 terms (S₂₀) = 20/2[2 x 4 + (20 - 1)(-3)] = 10[8 - 57] = -490

Find the sum of first 20 terms of an A.P. whose nth term is given by Tn = (7 - 3n).(A) 382(B) -490(C) 420(D) -382

Answer»

The correct option is: (B) -490

Explanation:

We have, T_n = (7 -3n)

First term, T₁ = (7 -3 x 1) = 4

Second term, T₂ = 7 - 3 x 2= 1

Third term, T₃ = 7 -3 x 3 = -2

.'. Series is 4, 1, - 2, ..........

and common difference = -3

Sum of first 20 terms (S₂₀)

= 20/2[2 x 4 + (20 - 1)(-3)] = 10[8 - 57] = -490