ALGEBRAIC IDENTITIES
ALGEBRAIC IDENTITIES
An identity is an equality that remains true regardless of the values chosen for its variables.
Algebraic Identities
- (a+b)2 = a2 + 2ab + b2
- (a-b)2 = a2 - 2ab + b2
= (3x)2 + 2(3x)(4y) + (4y)2
= 9x2 + 24xy + 16y2
2. Prove (a-b)2 = a2 - 2ab + b2
Solution:
(a - b)2 = (a-b) (a-b)
(a - b)2 = a(a-b) – b(a-b)
(a - b)2 = a2 – ab – ab + b2
(a - b)2 = a2 - 2ab + b2
EXAMPLE: 2
Expand (2a – 3b)2
Solution:
= (2a)2 – 2(2a)(3b) + (3b)2
= 4a2 – 12ab + 9b2
3. Prove (a+b)(a-b) = a2 – b2
Solution:
(a+b)(a-b) = a (a-b) + b (a-b)
(a+b)(a-b) = a2 – ab + ab – b2
(a+b)(a-b) = a2 – b2
EXAMPLE : 3
Expand (5x + 4y)(5x – 4y)
Solution:
= (5x)2 – (4y)2
= 25x2 – 16y2
4. Prove (x+a)(x+b) = x2 + (a+b)x +ab
Solution:
(x+a)(x+b) = x (x+b) + a (x+b)
(x+a)(x+b) = x2 + bx + ax + ab
(x+a)(x+b) = x2 + (a+b) x + ab
Example: 4
Expand (m+5)(m-8)
Solution:
= m2 + (5-8)m – (5)(8)
= m2 – 3m - 40