Observe the following pattern:

11 × 13 = (12 - 1) × (12 + 1) = 122 - 1

13 × 15 = (14 - 1) × (14 + 1) = 142 - 1

15 × 17 = (16 - 1) × (16 + 1) = 162 - 1

Using this pattern, find (i) 19 × 21 (ii) 29 × 31

Asked by Topperlearning User | 4th Jun, 2014, 01:23: PM

Expert Answer:

Using the given pattern, we have:

(i) 19 × 21= (20 - 1) × (20 + 1) = 202 - 1 = 400 - 1 = 399

(ii) 29 × 31= (30 - 1) × (30 + 1) = 302 - 1 = 900 - 1 = 899

Answered by  | 4th Jun, 2014, 03:23: PM