Question

In an ap if the 12th term is -13 and sum of first 4 terms is 24 what is the sum of first 10terms

Answer 1

Answer:

sum of first 10 terms=0

Step-by-step explanation:

Answer 2

Answer:

$a_n = a+(n-1)d$

$a_{12} = -13\\\Rightarrow a_{12} = a+11d\\\Rightarrow -13 = a+11d$    ...(1)

$S_n=\cfrac{n}{2}\big[2a+(n-1)d\big]\\\Rightarrow S_4 = 24\\\Rightarrow 24 = \cfrac{4}{2}\big[2a + 3d\big]\\\Rightarrow 2a+3d = 12    ...(2)$

Solving Eqns (1) and (2), we get

$a = 9 \text { and } b = -2$

Now,

$S_{10} = \cfrac{10}{2}\big[a + 9d]\big]\\\Rightarrow S_{10} = 5[9 + 9(-2)]\\\Rightarrow S_{10} = 5(9 - 18)\\\Rightarrow S_{10} = -45$

Step-by-step explanation: