Suppose an arithmetic sequence has

Question

A₈=-16 and a₁₆=-40, find a₁

Answer 1

Rauna

a_n = a + (n-1) d

So - 16 = a + 7d (1) and -40 = a + 16 d (2)

1. These come from substituting the values given.

2 simultaneous equations.

Subtract (1) from (2) and use this to find d.

When you know d, substitute back into (1) to find a = a₁

Mike