Question

The 6th term of an ap is zero prove that its 21st term is triple its 11th term

Answer 1

Answer:

Step-by-step explanation:

Hey friend, ☺ here is ur answer __________________________

a6 = 0

a + 5d = 0 .....…....(1)

a21 = a + 20d

= a + 5d + 15d

= 0 + 15d ( from (1) )

a21 = 15d

a11 = a + 10d

= a + 5d + 5d

= 0 + 5d ( from (1) )

a11 = 5d...............(2)

we can also write a21 as :-

a21 = 15d

= 3 × 5d

a21 = 3 + a11. from (2)

hence proved

Answer 2

Answer:

First term = a

Common diff. = d

6th term = a + 5d

a + 5d = 0

a = -5d

21st term = a + 20d = -5d + 20d = 15d

11th term = a + 10d = -5d + 10d = 5d

Therefore,

21st term = 3 * 11th term = 3 * 5d = 15d (proved)