Question

the first and last term of an ap be A and L show that the sum of the n terms from the beginning and n
term from the end is equals to a + l

Answer 1

we have,
$sn = 1 \div 2(2a + (n - 1)d$
or, Sn = 1/2( a + (a + (n-1)d )
or, Sn = 1/2( a + l ).
since, a + (n-1)d = last term(l)