Question

determine o numero de termos da PA (1,4,7,...,298)

Answer 1

An=A1+(n-1).r
298=1+(n-1).3
298=1+3n-3
298+2=3n
3n=300
n=100

Answer 2

$a_n=a_1+r(n-1)\\r=4-1=3\\298=1+3(n-1)\\297=3(n-1)\\\\\dfrac{297}{3}=n-1\\\\99=n-1\\n=100$