Question

in an ap, if S5+S7= 167 and S10=235, then find the ap, where Sn denotes the sum of first n terms

Answer 1

5n2-3n is the sum of first n terms

Answer 2

Answer:

Step-by-step explanation:

here,

    s10 = 235

=> 10/2 x [ 2a + 9d] = 235

=> 2a + 9d = 47.....................(i)

now,

  s5 + s7 = 167

=>5/2 [ 2a + 4d ] + 7/2 [ 2a + 6d ] = 167

=>5a + 10d + 7a + 21d = 167

=>12a + 31d = 167.....................(ii)

from (i) & (ii),

d = 5

thus,

a = 1 .........................[from (i)]

thus the AP is--

1,6,11,16.............