Respuesta :
Answer:
Below in bold.
Step-by-step explanation:
I'll find the first term and the sum of 20 terms.
This is an arithmetic series whose 20th term = 97.
nth term (an)= a1 + (n - 1)d where a1 = first term, so:
97 = a1 + (20 - 1)*5
a1 = 97 - 19*5 = 97 - 95
So the First term (a1) = 2.
Sum of 20 terms = (n/2)[a1 + L] where L = the last term.
Sum of 20 terms = (20/2) [2 + 97]
= 990.
Sum of 20 term is 990
Given that;
Number of term = 20
Last term = 97
Common difference = 5
Find:
Sum of 20 term
Computation:
An = a + (n - 1)d
97 = a + (20 - 1)5
97 = a + 95
a = 2
Sum of term = [n/2][2a + (n - 1)d]
Sum of 20 term = [20/2][2(2) + (20 - 1)5]
Sum of 20 term = [10][4 + 95]
Sum of 20 term = [10][99]
Sum of 20 term = 990
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