Question

Plz ans it...fast ... it's urgent

Answer 1

Here is your solution :

Given,

First term ( a ) = ( -8 )

Sum of n terms = 52

Common difference( d ) = ( -6 ) - ( -8 ) = -6 + 8 = 2.

Let the number of terms is n.

No. of terms = n.

=> Sum of n terms = ( n/2 ) [ 2a + ( n - 1 )d ]

=> 52 = ( n/2 ) [ 2 × ( -8 ) + ( n - 1 )2 ]

=> 52 × 2 = n [ -16 + 2n - 2 ]

=> 104 = n ( 2n - 18 )

=> 104 = 2n² - 18n

=> 2 × 52 = 2( n² - 9n )

=> 52 = n² - 9n

=> n² - 9n - 52 = 0

=> n² - 13n + 4n - 52 = 0

=> n( n - 13 ) + 4 ( n - 13 ) = 0

=> ( n - 13 ) ( n + 4 ) = 0

•°• n = 13 or -4

Since, number of terms in an A.P. can't be negative.

So, n = 13.


b. ) 13