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Arithmetic Progressions

Question 3:

In the following APs find the missing term in the boxes

I.

II.

III.

IV.

V.

Answer:

I.

For this A.P.,

a = 2

a3 = 26

We know that, an = a + (n − 1) d

a3 = 2 + (3 − 1) d

26 = 2 + 2d

24 = 2d

d = 12

a2 = 2 + (2 − 1) 12

= 14

Therefore, 14 is the missing term.

II.

For this A.P.,

a2 = 13 and

a4 = 3

We know that, an = a + (n − 1) d

a2 = a + (2 − 1) d

13 = a + d (I)

a4 = a + (4 − 1) d

3 = a + 3d (II)

On subtracting (I) from (II), we obtain

−10 = 2d

d = −5

From equation (I), we obtain

13 = a + (−5)

a = 18

a3 = 18 + (3 − 1) (−5)

= 18 + ...

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