Step-by-step explanation:
From the given question it appears that (n-1) is in the numerator's place, if it is so, then let us solve it.
[tex]a_n = - 2 + \frac{3}{2}(n - 1) \\ \\ \therefore \: a_{21} = - 2 + \frac{3}{2} (21 - 1) \\ \\ \therefore \: a_{21} = - 2 + \frac{3}{2 } \times \: 20\\ \\ \therefore \: a_{21} = - 2 + 3 \times \: 10 \\ \\ \therefore \: a_{21} = { -2 + 30} \\ \\ \therefore \: a_{21} = 28 \\ \\ \huge \red{ \boxed{\therefore \: a_{21} = 28} } \\ \\ [/tex]
