Question

V
(iv) If five times the 5th term of an A.P. is equal to eight times its 8th term, then
show that its 13th term is zero.​

Answer 1

Answer:

ATQ

we know an = a + (n-1)d

5a5 = 8a8

5(a + 4d) = 8(a + 7d)

5a + 20d = 8a + 56d

3a + 36d = 0

a + 12d = 0

we know

a13 = a + 12d = 0

then

a13 = thirteenth term = 0

hope this will help you

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Answer 2

Step-by-step explanation:

5*a5 = 8*a8

5* (a + 4d) = 8* (a + 7d)

5a + 20d = 8a + 56d

3a = - 36d

a = - 12d -------Eq.(1)

Now,

a13 = a + 12d

= -12d + 12d ( from equation 1 )

= 0

Hence Proved.

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I hope this helps you :)