Evaluate each of the following using identities: (i) (2x –1x)2 (ii) (2x + y) (2x – y) (iii) (a2b – b2a)2 (iv) (a – 0.1) (a + 0.1) (v) (1.5.x2 – 0.3y2) (1.5x2 + 0.3y2) -Maths 9th

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Answer :

(i) (2x – 1/x)2 [Use identity: (a - b)2 = a2 + b2 - 2ab ] (2x – 1/x)2 = (2x) 2 + (1/x)2 - 2 (2x)(1/x) = 4x2 + 1/x2 - 4 (ii) (2x + y) (2x – y) [Use identity: (a - b)(a + b) = a2 - b 2 ] (2x + y) (2x – y) = (2x ) 2 – (y)2 = 4x2 - y 2 (iii) (a2b – b 2a)2 [Use identity: (a - b)2 = a2 + b2 - 2ab ] (a2b – b 2a)2 = (a2b) 2 + (b 2a)2 - 2 (a 2b)( b 2a) = a 4b 2 + b 4a 2 - 2 a 3b 3 (iv) (a – 0.1) (a + 0.1) [Use identity: (a - b)(a + b) = a2 - b 2 ] (a – 0.1) (a + 0.1) = (a) 2 – (0.1)2 = (a) 2 – 0.01 (v) (1.5 x 2 – 0.3y2 ) (1.5 x 2 + 0.3y2 ) [Use identity: (a - b)(a + b) = a2 - b 2 ](1.5 x 2 – 0.3y2 ) (1.5x2 + 0.3y2 ) = (1.5 x 2 ) 2 – (0.3y2 ) 2 = 2.25 x4 - 0.09y4

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