Question

If the 3rd & 9th term of an AP are -4 & -8 respectively which term of this AP is Zero

Answer 1

Heya mate!!

The question is wrong and the 3rd and 9th terms should respectively be -4 and 8.

Then here's your answer!!

Given that,

a + 2d = -4

=> a = (-4 - 2d)-------(i)

Also,

a + 8d = 8

Substituting (i) in the equation,

=> -4 - 2d + 8d = 8

=> 6d = 12

=> d = 2

Then,

a = -4 - 2d = -4 - (2 x 2) = -4 - 4 = -8

Nth term of the AP = 0

=> a + (n - 1) d = 0

=> -8 + (n - 1) x 2 = 0

=> 2 (n - 1) = 8

=> n - 1 = 4

=> n = 5

Therefore the 5th term of this AP is 0.

Hope it helps you!!!

Cheers :)

#foreverJungkook

Answer 2

$a + 2d = - 4$

$a + 8d = - 8$

by solving those equation.

$a = - 8 \div 3$

$d = - 2 \div 3$

for n term is 0

$a + (n - 1)d = 0$

$- 8 \div 3 + (n - 1) \times (- 2 \div 3)$ =0

$(n - 1)( - 2 \div 3) = 8 \div 3$

$- 2n \div 3 + 2 \div 3 = 8 \div 3$

$- 2n \div 3 = 8 \div 3 - 2 \div 3$

$- 2n \div 3 = 6 \div 3$

$- 2n = 6 \\ n = 6 \div - 2 \\ n = 3$

3rd term of AP is 0