Question

please some one help me with this sum.

Answer 1

see,

19th term is 52,

∴ a + 18d = 52        ... (i)

& 38th term is 128,

∴ a + 37d = 128     ... (ii)

⇒ subtract (i) from (i)

a + 18d = 52

a + 37d = 128

-      -         -

_____________

     -19d = -76

          d = 4

now, put value of d in (i)

a + 18d = 52

a + 18×4 = 52

a + 72 = 52

a = 52 - 72

a = -20

for sum of 1st 56 terms -

put the formula of sum of nth terms and put -

n = 56

a  = -20   &

d = 4

and your answer will come...

Hope it helps you.. :-)

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