Given the explicit formula, find the term in each problem.
1. an=9n-12 find a40
2. an=2 * (-5)^n-1 find a9

Jonathan can type 20 documents in 40 minutes ,and susan can type it in 30 minutes and jack can type it in 24 minutes working together ,how much time will it is take them type the same document

Given: △acm, m∠c=90°, cp ⊥ am , ac: cm=3: 4, mp-ap=1. find am.

If set d is not the empty set but is a subset of set e, then which of the following is true? d ∩ e = d d ∩ e = e d ∩ e = ∅