Question

if the sum of the first 12terms of an A.P. is 138 and its first term is 17​

Answer 1

Hey mate, here is your answer..........

a=17

S12=138

n=12

$s12 = \frac{12}{2} \times (17 + 17 + (12 - 1))d$

$138 = 6 \times (34 + 11d)$

$\frac{138}{2} = 34 + 11d$

$23 - 34 = 11d$

therefore,

$d = - 1$

A12=17+(12-1)(-1)

=17+(11×-1)

=17-11

=6

Hope this helps you.....