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Coordinate Geometry

Question
CBSEENMA9001818

 Multiply 9x2 + 25y2 + 15xy + 12x -20y + 16 by 3x - 5y - 4 using suitable identity.

Solution

(3x - 5y - 4) (9x2 + 25y2 + 15xy + 12x - 20y + 16)
= {(3x) + (-5y) + (-4)} {(3x)2 + (-5y)2 + (-4)2 - (3x) (-5y) - (-5y) (-4) - (-4) (3x)}
= (3x)3 + (-5y)3 + (-4)3 - 3 (3x) (-5y) (-4)
= 27x3 - 125y3 - 64 - 180cy.