Question

if the 10th term of an A.Pis 38 and the 16th term is 74. Find the sum of the first 20th terms of A.P ​

Answer 1

$10th \: term = 38 \\ a + 9d = 38 - - - - - equcation1\\ \\ \\ 16th \: term = 74 \\ a + 15d = 74 - - - - - - - equcation2$

the general form of the Ap is a,a+d,a+2d,a+3d...........

from equation 1 and 2

9d-15d=38-74

-6d=-36

6d=36

d=6

subtistude d value in equation 1

a+9d=38

a+54=38

a=38-54

a= -16