Answer:
120
Step-by-step explanation:
[tex]nth = a + (n - 1)d[/tex]
that above is the formula for nth term.
since a is the first term then a =3 , n is 21 , and d which is the common difference is going to be 2. since d is gotten by 5-3, 7-5 , 9-7.
with all the parameters,
21st term = 3(21-1)2
=3(20)2
=3×20×2
= 120
therefore the 21st term is 120
