Question

how many terms are there in the AP -12 , -7............133? find the sum of the last two terms​

Answer 1

Step-by-step explanation:

nth term = a + ( n - 1 )d,

Where a is the first term and d is the common difference.

Here,

First term = - 12

Com. Dif. = - 7 - (-12) = 5

Let 133 be the nth term:

= > 133 = - 12 + ( n - 1 ) 5

= > 133 + 12 = ( n - 1 )5

= > 145 = ( n - 1 )5

= > 29 = n - 1

= > 29 + 1 = n

= > 30 = n

133 is the 30th term.

Last two terms = 30th & 29th

Their sum:

= > 133 + a + (29-1)d

= > 133 - 12 + (28)5

= > 121 + 140

= > 261