Question

In A.P.if the 12th term is -13and the sum of its first four terms is 24.find the sum of its first 10 terms

Answer 1

Here given a12= -13 and s4 = 24..let d be the common difference.
Now a + 11d = -13.........(1)
also, 4/2(2a + 3d)=24
or..... 2(2a+ + 3d)=24
or..... 2a + 3d = 12........(2)
Now multiplying eq.(1) with 2,we get
2a + 22d =-26.....(3)
Now subtracting eq.(3) from (2),we get
2a + 22d = -26
-2a +(-) 3d = (-) 12........19d = -38 i.e. d = -2.
now putting the value of d in eq. 1 we get
a + 11(-2) = -13 i.e. a = -13 +22 i.e. a = 9.
So s10 = 10/2{2×9+9(-2)}
= 5 (18-18) = 5(0) = 0.
Hope it helps.......

Answer 2

Answer:

Be happy may help you