Find sum of -3,2,7,12....,132 Arithmetic series

1 answer:

8 0

$a_1=-3 \\
d=2-(-3)=5 \\
a_n=132 \\ \\
a_n=a_1+d(n-1) \\
132=-3+5(n-1) \\
132=-3+5n-5 \\
132=-8+5n \\
140=5n \\
n=28 \\ \\
S_n=\frac{n(a_1+a_n)}{2} \\
S_{28}=\frac{28(-3+132)}{2}=\frac{28 \times129}{2}=14 \times 129=1806$

The sum is 1806.

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