Question

please help me with this as soon as possible.​

Answer 1

General term of any AP series is given by :

Tn = a + (n-1)d ...(1)

where,

a - first term.

d - common difference and

n - nth term

now accurding to your सवाल

T4 = 19

T7 = 40 from formulae ...(1)

T4 = a + 3d = 19

T7 = a + 6d = 40

now from above two equations in a and d after solving you'll get,

a = -2

d = 7.

Now sum of n terms of any AP whose first term a and common difference d is given by :

Sn = n(2a + (n-1)d)/2 ...(2)

also accirding to question we have to find sum of 23 terms since here n = 23.

put finded values of a and d in equation ...(2) you'll get ,

S23 = 1725.

AAH BTW I HAD NOT USED CALCULATOR MAYBE MY CALCULATION FOR SUM MAYBE WRONG BUT CONCEPT IS CORRECT YOU CAN 100% TRUST ON MY COBCEPT.