Question

Find the number of terms of the AP-12,-9,-6_,_,_, 12 if one is added to each term of this AP then find the sum of all terms of the AP thus obtained

Answer 1

the new A.P. formed :-
-11,-8,-5......13
S=n/2[2a+(n-1)d]
=9/2[2(-11)+(8)(3)]
=9/2[-22+24]
=9/2[2]
=9