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Mathematics

Factorise the following using appropriate identities:

(i) 9x2 + 6xy + y2

(ii) 4y2 - 4y + 1

(iii) x2(y2100)x^2 - \Big(\dfrac{y^2}{100}\Big)

Polynomials

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Answer

(i) 9x2 + 6xy + y2

[∵ a2 + 2ab + b2 = (a + b)2]

= (3x)2 + 2(3x)(y) + (y)2

= (3x + y)2

Hence, 9x2 + 6xy + y2 = (3x + y)(3x + y)

(ii) 4y2 - 4y + 1

[∵ a2 - 2ab + b2 = (a - b)2]

= (2y)2 - 2(2y)(1) + (1)2

= (2y - 1)2

Hence, 4y2 - 4y + 1 = (2y - 1)(2y - 1)

(iii) x2(y2100)x^2 - \Big(\dfrac{y^2}{100}\Big)

[∵ a2 - b2 = (a - b)(a + b)]

x2(y2100)=x2(y10)2=(xy10)(x+y10)x^2 - \Big(\dfrac{y^2}{100}\Big) \\[1em] = x^2 - \Big(\dfrac{y}{10}\Big)^2 \\[1em] = \Big(x - \dfrac{y}{10}\Big) \Big(x + \dfrac{y}{10}\Big)

Hence, x2(y2100)x^2 - \Big(\dfrac{y^2}{100}\Big) = (xy10)(x+y10)\Big(x - \dfrac{y}{10}\Big) \Big(x + \dfrac{y}{10}\Big)

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