Question

in an ap if common difference 2 sum of n terms is 49 7th term is 13 then n

Answer 1

✨d=2

Sn=49

A7=13

Sn=n/2(2a+(n-1)d)

A7=a+6d

13=a+12

✨a=1✨

now put this a in Sn equation.

49=n/2{2×1+(n-1)2}

$49 = \frac{n}{2} (2 + (n - 1)2) \\ 49 = \frac{n}{2} (2 + 2n - 2) \\ 49 = \frac{n}{2} \times 2n \\ 49 = {n}^{2} \\ n = 7$
✨Value of n=7

Answer 2

Answer:

=> n=7

Step-by-step explanation:

An A.P. is given .

comman difference (d) = 2

sum of n terms = 49

And 7th term = 13

To find the value of n.

As per question ,

by using the formula Tₙ = a + (n-1)d

T₇ = a + (n-1)d

13 = a + (7-1)2

13 = a + 6×2

13 = a + 12

a = 13 - 12

a = 1.

by using the formula

Sₙ=$\frac{n}{2} (2a+(n-1)d$

$\frac{n}{2}(2*1 + (n-1)2\\ \\\frac{n}{2}(2+2n-2)=49\\ \\\frac{n}{2}(2n)=49\\ \\n^{2}=49\\ \\n = +-7$

Here n = 7, because terms are positive not negatives.

Therefore, n = 7 .

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