Find the sum : (-3)+(-7)+(-11)+.........to 31 terms
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0
Answer:
-21 is the answer......
Answered by
2
Answer:
AP : 3, 7, 11,....., to 10 terms.
Here, we have ;
First term (a) = 3
Number of terms (n) = 10
Difference (d) = 7 - 3 = 4
Sum of n terms is given by formula :
\begin{gathered}\bf S_n = \frac{n}{2}[2a +(n-1)d] \\ \\ \bf S_{10} = \frac{10}{2}[2 \times 3+(10-1)4] \\ \\ \bf S_{10} = 5 [6 + 9 \times 4] \\ \\ \bf S_{10}= 5[6 + 36] \\ \\ \bf S_{10}= 5 \times 42 \\ \\ \red{\boxed{\bf S_{10} = 210}}\end{gathered}
S
n
=
2
n
[2a+(n−1)d]
S
10
=
2
10
[2×3+(10−1)4]
S
10
=5[6+9×4]
S
10
=5[6+36]
S
10
=5×42
S
10
=210
please mark as brainlist
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