Question

if 3x-4y = 16 and xy=4, find the value of 9x*2+16y*2

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Answer 1

we know , ( a-b )² = a² + b² - 2ab .......... (1)

using (1) ,

=> ( 3x - 4y ) ² = 16²

=> 9x² + 16y² - 24xy = 256

=> 9x² + 16y² = 256 + 24 (4). { xy = 4 , given }

=> 9x² + 16y² = 256 + 94 = 350