Question

In an A.P a10= 20, a20=10.Find a30 ?
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Answer 1

Answer:

a30 = 0

Step-by-step explanation:

a10 = 20   -->  a + 9d = 20 ----> (1)

a20 = 10   -->  a + 19d = 10 ---->(2)

Subtracting (1) from (2),

10d = -10

d = -1

Substituting d value in (1),

a - 9 = 20

a = 29

Therefore,

a30 = a + 29d = 29 +29(-1) = 29 - 29

a30 = 0

Hope it is useful...

Answer 2

a10= a+9d= 20......(i)

a20= a + 19d= 10.....(ii)

Subtracting (i) from (ii)

10d= -10

d= -1

Putting value of d in (i)

20= a -9

hence a= 29

hence a30 = a+29d

29-29=0