Extra Questions For Class 9 Maths Polynomials | Q3

Question 3: Using suitable identity evaluate the following:
(i) 98³
(ii) 188 × 212

Video Explanation

Explanatory Answer | Chapter 2 Extra Question 3

(i) (98)³

(98)³ = (100 - 2)³
(100 - 2)³ is of the form (a - b)³
(a - b)³ = a³ - 3a²b + 3ab² - b³
So, (100 - 2)³ = 100³ - 3 × 100² × 2 + 3 × 100 × 2² - 2³
= 1,000,000 - 60,000 + 1200 - 8 = 9,41,192

(ii) 188 × 212

188 × 212 = (200 - 12)(200 + 12)
The expression is of the form (a - b)(a + b)
(a - b)(a + b) = a² - b²

So, (200 - 12)(200 + 12) = 200² - 12²
= 40,000 - 144 = 39856