Math, asked by sharmayogesh040871, 8 months ago

Find the sum : (-3)+(-7)+(-11)+.........to 31 terms

Answers

Answered by prajwalbenare
0

Answer:

-21 is the answer......

Answered by rimpithakur85
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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