1.

If the pth term of a.p. is 4p-1,find the 40th term and su of first 40 terms

Answer»

EXPLANATION.

  • GIVEN

Pth TERM of Ap = 4p - 1

FIND 40TH TERM AND SUM OF 40 TERM.

let we can put the value of p = 1,2,3,....

put p = 1

we get,

4(1) - 1 = 3

put p = 2

we get,

4(2) - 1 = 7

put p = 3

we get,

4(3) - 1 = 11

put p = 4

4(4) - 1 = 15

the series can be WRITTEN as = 3,7,11,15.....

let first term = a = 3

common difference = d = b - a = 7 - 3 = 4

Nth term of ap = a + ( n - 1 ) d

40th = a + 39d

3 + 39(4)

3 + 156 = 159

Sn term of Ap = n/2 ( 2a + ( n - 1 ) d)

S40 = 40/2 ( 2(3) + 39 X 4 )

20 X 6 + 156

20 X 162 = 3240



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