Question

How many terms of the AP :
3,5,7,9,....... must be taken to give a sum of 63 ​

Answer 1

Answer:

7 terms

Step-by-step explanation:

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

63=n/2(6+(n-1)2)

126=n(6+2n-2)

126=n(4+2n)

126=4n+2n^2

2n^2+4n-126=0

n^2+2n-63=0

n^2+9n-7n-63=0

n(n+9)-7(n+9)=0

(n-7)(n+9)=0

n=7 or -9

-9 terms are not possible.

so answer is 7

Answer 2

Answer:

7

Step-by-step explanation:

63=n/2(6+n-1)2)

126-n(6+2n-2)

126=4n(4+2n)

126=4n+2n^2

2n^2-4n-126=0

n^2+2n-63=0

n^2 2+9n-7n+9=0

n(n-7)-7(n+9)=0

(n+7)(n+9)=0

n=7,-9