Prove that $ u_1 + u_5 = 2u_3 $.

Question

$u_n$ is an arithmetic progression which is an increasing sequence.

Prove that $$ u_1 + u_5 = 2u_3 $$

is it correct to rely on the law that states that $a + c = 2b$.

Answer 1

$u_5 = u_1 + 4d$

$u_3 = u_1 + 2d$

So $u_1 + u_5 = 2u_1 + 4d = 2(u_1 + 2d) = 2u_3$