Question

Class 10


Find the sum of AP - 9,17,25... to 12 terms.

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Answer 1

$\huge\mathfrak\green{Solution}$

• Given that :

a = 9

d = 17-9 = 8

n = 12

We know that,

an = a + (n-1) d

an = 9 + (12-1) 8

an = 9 + 88

an = 97

Thus the 12th term of the A.P is 97 .

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Answer 2

Answer:

636

Step-by-step explanation:

AP : 9, 17, 25,....., to 12 terms.

Here, we have ;

First term (a) = 9

Number of terms (n) = 12

Difference (d) = 17 - 9 = 8

Sum of n terms is given by formula :

$\bf S_n = \frac{n}{2}[2a +(n-1)d] \\ \\ \bf S_{12} = \frac{12}{2}[2 \times 9+(12-1)8] \\ \\ \bf S_{12} = 6[18 + 11 \times 8]\\ \\ \bf S_{12}= 6 \times 106 \\ \\ \red{\boxed{\bf S_{10} = 636}}$

Hence, the sum of the given AP is 636.