Question

5th term of an ap is equal to 3 times the 2nd term if 7th term is 4 less than two times the 4th term, find the 12th term​

Answer 1

a

3

=7 a

7

=3a

3

+2

a

7

=3×7+2=23

a+2d=7→(1)

a+6d=23→(2)

__________________

−4d=16

d=4→(3)

Sub (3) in (1)

a+2×4=7

a+8=7⇒a=−1

S

n

=

2

n

(2a+(n−1)d)

S

20

=

2

20

(2×−1+(20−1)4)

S

20

=10(76−2)

S

20

=10×740

S

20

=740

NOBITA221✔