Question

sum of first 11 term of Ap is 19 is sum if first 19term is 11 find of sum of first 3oterm d.​

Answer 1

Answer:

-36480/143

If the question is true, then

Step-by-step explanation:

let, 1st term = a, common difference = d

Given,

S11 = 19, t19 = 11, then S30 = ?

Now,

t19 = a+18d = 11. ---eqⁿ1

S11 = 11/2.[2a+10d] = 19

or, 2a+10d = 38/11

or, a+5d = 19/11. ---eqⁿ2

On solving both the equations,

a = -263/143 and d = 102/143

Now,

S30 = 30/2[2x(-263/143) + 29x102/143]

= 15x[-526/143+2958/143]

= 15x-2432/143 = -36480/143.