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Mathematics

Using standard formulae, expand each of the following:

(i) (2a2 + 3b)2

(ii) (3x2y + z)2

(iii) (2x+13x)2\Big(2x + \dfrac{1}{3x}\Big)^2

Expansions

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Answer

We know that,

⇒ (a + b)2 = a2 + b2 + 2ab.

(i) Given,

⇒ (2a2 + 3b)2

⇒ (2a2)2 + (3b)2 + 2 × 2a2 × 3b

⇒ 4a4 + 9b2 + 12a2b

Hence, (2a2 + 3b)2 = 4a4 + 9b2 + 12a2b .

(ii) Given,

⇒ (3x2y + z)2

⇒ (3x2y)2 + (z)2 + 2 × 3x2y × z

⇒ 9x4y2 + z2 + 6x2yz

Hence, (3x2y + z)2 = 9x4y2 + z2 + 6x2yz .

(iii) Given,

(2x+13x)2(2x)2+(13x)2+2×2x×13x4x2+19x2+43\Rightarrow \Big(2x + \dfrac{1}{3x}\Big)^2 \\[1em] \Rightarrow (2x)^2 + \Big(\dfrac{1}{3x}\Big)^2 + 2 \times 2x \times \dfrac{1}{3x} \\[1em] \Rightarrow 4x^2 + \dfrac{1}{9x^2} + \dfrac{4}{3}

Hence, (2x+13x)2=4x2+19x2+43\Big(2x + \dfrac{1}{3x}\Big)^2 = 4x^2 + \dfrac{1}{9x^2} + \dfrac{4}{3}.

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