Question

The fifth term of an A.P. is 20 and the sum of seventh and eleventh terms is 64. Determine A.P​

Answer 1

a5th =20 (given)

=> a+(5-1)d=20

=>a+4d=20 ......(1)

a7th + a11th =64 (given)

=>a+6d+a+10d=64

=>2a+16d=64

=>2(a+8d)=64

=>a+8d=64/2

=>a+8d =32 ......(2)

Substract (1) equation from (2) ,

a+8d-(a+4d)=32-20

=>a+8d-a-4d=12

=>4d=12

=>d=3(Answer)

Answer 2

Answer:

Mark me as Brainliest

Step-by-step explanation:

Here, a5=20

=>a+4d=20 - (1)

And, a7+a11=64

=>a+6d+a+10d=64

=>2a+16d=64

=>a+8d=32 - (2)

Solving eqn. (1) and(2), we get

a+4d=20

a+8d=32

=> - 4d= - 12

=> d= - 12/-4

=> d= 3

Putting d in eqn. (1),

a+4d=20

=>a+4×3=20

=>a+12=20

=>a=20-12

=>a=8

Hence, the AP will be 8, 11, 14, 17