Question

IN an AP if the 12th term is -13 and the sum of four terms is 24 what is the summ of the first 10 terms?

Answer 1

nth term = a + (n-1)d

Sn = n/2{a + (n-1)d}

12th term = a + 11d = -12 ........ (i)

S4 = 4/2{a + 3d) = 24

a + 3d = 12 ....... (ii)

From (i) a + 11d = -12

a = -11d - 12 Substitute this in (ii)

-11d - 12 + 3d = 12

-8d = 24

d = -3

a = -11d -12 = -11x-3 - 12 = 21

S10 = 10/2 {21 + (10-1)X-3}

= 5 (21 -27)

= 5 X -6

= -30

Answer 2

Answer:

0

Step-by-step explanation:

a(12) = -13

s(4) = 24

s(10)= ?

a+11d = -13........................(i)

n/2(2a+(n-1)d) = 24

2a+3d = 12.......................(ii)

multiply equation (i) by 2 and then subtract by equation(ii)

we get...

a = 9, d = -2

Now ,,

s(10) = 10/2[2 x 9+ (10 - 1) -2]

= 5 x 0 = 0