Answer:
[tex]T_{21} = 53[/tex]
Step-by-step explanation:
Given
[tex]a = -7[/tex]
[tex]d = 3[/tex]
Required
Determine [tex]T_{21}[/tex]
This is calculated using sum of Ap formula
[tex]T_n = a + (n - 1)d[/tex]
In this case:
[tex]n =21[/tex]
So, the equation becomes
[tex]T_{21} = -7 + (21 - 1) * 3[/tex]
[tex]T_{21} = -7 + 20 * 3[/tex]
[tex]T_{21} = -7 + 60[/tex]
[tex]T_{21} = 53[/tex]
