Question

D=-2 , a22=-39 find a?

Answer 1

d = - 2 

$a_{22} = a + 21d \\ \\ -39 = a + 21(-2) \\ \\ -39 = a - 42 \\ \\ a = - 39 + 42 \\ \\ a = 3$

Answer 2

I hope all steps are clear