Question

If 7 times the 7th term of an AP is equal to 11 times its 11th term , show that the 18th term of the AP is 0​

Answer 1

Answer:

Step-by-step explanation:

7(a7) = 11(a11)

=> 7 (a + 6d) = 11 ( a + 10d)

=> 7a + 42d = 11a +110d

=> -4a = 68d

=> a = -17d

=> -a = 17d -----------(1)

a18 = a + 17d ( from 1)

=> a18 = a + (-a)

=> a18 = 0

Answer 2

Answer:

Step-by-step explanation:

7(a7)      =         11(a11)

7(a+6d) = 11(a+10d)

7a+ 42d = 11a + 110 d

7a - 11a = 110 d -42 d

-4 a = 68 d

-4/68 = d/a

-1/17 = d/a

∴a= 17

 d = -1

to prove a18 = 0

a18 = a+ 17d

a18= 17 + 17 × -1

a18 = 17 - 17

∴a18=0

hope it helps u