Use the Product (A + B) (A – B) = A2 – B2 to Evaluate: 21 X 19

Use the product (a + b) (a – b) = a² – b² to evaluate:
21 x 19

Sum

21 x 19 = (20+1) (20−1)

= (20)² − (1)²

= 400 − 1

= 399

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Product of Sum and Difference of Two Terms

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Chapter 12: Identities - Exercise 12 (A) [Page 150]

Chapter 12 Identities
Exercise 12 (A) | Q 4.1 | Page 150

Evaluate : (a+b) (a−b) (a²+b²)

Use the product (a + b) (a – b) = a² – b² to evaluate:
33 x 27

Use the product (a + b) (a – b) = a² – b² to evaluate:
9.8 x 10.2

Use the product (a + b) (a – b) = a² – b² to evaluate:
7.7 x 8.3

Evaluate : `("a"/(2"b")+(2"b")/"a")("a"/(2"b")-(2"b")/"a")`

Evaluate : (5x + 8y) (3x + 5y)

Evaluate : (9a − 7b) (3a − b)

Evaluate: (a² + 5) (a² − 3)

Evaluate: (3x + 4y) (3x − 4y) (9x² + 16y²)

Evaluate: (a + bc) (a − bc) (a² + b²c²)