Question

If 5, 7 and 9 are in A.P., then which of the following is in A.P.?

विकल्प

• 5 × 7, 7 × 9 and 9 × 5

• 5 × 7, 7 × 7 and 9 × 7

• 2 × 5, 2 × 9 and 5 × 9

• 5 – 7, 7 – 9 and 9 – 5

Answer 1

5 × 7, 7 × 7 and 9 × 7

Explanation:

We know that, if a, b, c, ...... are in A.P.

Then ka, kb, kc, ...... are also in A.P.

Since 5, 7, 9 are in A.P.

Then 5 × 7, 7 × 7, 9 × 7 are also in A.P.  ...[Here 49 – 35 = 63 – 49 = 14]