Question

qual o numero de termos da PA: (100,98,96,...,22)

Answer 1

an=a1+(n-1).R
22=100+(n-1).-2
22=100+2n+2
2n=22-102
n=80/2
n=40

Answer 2

100=22+(n-1)2
100=22+(-2n)2 
2n=22+2-100
2n=24-100
n=76÷2=38