Question

in an ap if the 12th term is minus 13 and the sum of the first 4 term is 24 what is the sum of the first 10th term use formula method

Answer 1

t12=-13,a+11d=-13, a=-13-11d
s4=n/2(2*a+(n-1)*d)
24=4/2(2*a+(4-1)*d)
24 =2(2*a+3*d)
24/2=2*a+3*d
12=2*a+3*d
12=2*(-13-11d)+3*d
12=-26-22d+3d
12+26=-19d
-38/19=d; d=-2
a=-13-11d
=-13-11×-2
=-13+22
=9
s10=10/2(2*9+(10-1)*-2)
=5(18+9*-2)
=5(18-18)
=5*0
s10=0