Question

which term of the ap 21,18,15,...is -81​

Answer 1

Question:-

Which term of the ap 21 , 18 , 15 ......... is - 81

Solution:-

$\bf \: T_n \: = \: a \: + (n \: - 1)d$

Given

$\rm \: T_n = - 81$

$\rm\: first \: \: term \: (a) = 21$

$\rm \: common \: \: difference \: (d) = 18 - 21 = - 3$

Now put the value on formula

$\bf \: T_n \: = \: a \: + (n \: - 1)d$

$\rm \: - 81 = 21 + (n - 1) \times - 3$

$\rm \: - 81 = 21 - 3n + 3$

$\rm \: - 81 = 21 - 3n$

$\rm \: - 81 - 21 = - 3n$

$\rm \: - 102 = - 3n$

$\rm \: n = \frac{102}{3}$

$\rm \: n \: = 34$

Number of term is 34

Answer 2

Answer:

the numbers of term is 34