Question

4. In an A.P. 19 th term is 52 and 38th term is 128, find sum of first 36 terms.

how to solve
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Answer 1

HEYA MATE HERE'S YOUR REQUIRED STEPS:-

19th term:- a+18d=52----1 [a is the first term

and d is the

common difference]

a+37d =128--- 2

Solving equations(by subtracting) 1 and 2 we get:-

-19d= -76

d= (-76)/(-19)

Therefore, d=4

Replacing the value of d,in equation 1 we get:-. a+18×4=52

So, a=52-72

So, a=-20

Now, using the formula S36=n/2(2a+(n-1)d)

=36/2(2×(-20)+35×4)

=18(-40+140)

=18(100)

Therefore sum of 36th term=1800

HOPE THIS HELPS..☺️