Question

If in an AP ,If 12th term is -13,and the sum of first four terms is 24, what is the sum of first four terms?

Answer 1

hi dear,
here is ur answer..........................
12th term=a+11d=-13...........................1.
a+a+d+a+2d+a+3d=24
4a+6d=24
2a+3d=12
2(-13-11d)+3d=12                      (from 1..)
-26-22d+3d=12
19d=-38
d=-2
a=-13-11(-2)=9
now sum of four terms=2(2*9+3(-2))
                                    =2(18-6)
                                    =2(12)
                                    =24
HOPE IT HELPS UH..........................
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