Find the explicit formula for the recursive sequence using backtracking

d1 = 3

dn= -2dn-1

I’m thinking I will have (-6, 12, -24, 48,…..)

dn = -2dn-1

= -2dn-1 + 1

= -2 (-2dn-1 +1) +1

but I do not know what else to do to end with a formula. Please show me what my formula will be

* all the (n-1) should be subscripts, do know how to get it to subscript here in this window