Question 18Square of 9x−7xy isa 81x2+49x2y2b 81x2−49x2y

| Question 18

Square of

9 x - 7 x y

is
a)

81 x^{2} + 49 x^{2} y^{2}

81 x^{2} - 49 x^{2} y^{2}

81 x^{2} + 49 x^{2} y^{2} - 126 x^{2} y

81 x^{2} + 49 x^{2} y^{2} - 63 x^{2} y

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Right Answer is:

SOLUTION

c) $81 x^{2} + 49 x^{2} y^{2} - 126 x^{2} y$
$\to$ Square of $(9 x - 7 x y) = (9 x - 7 x y)^{2}$
Comparing with $(a - b)^{2}$ , we get $a = 9 x$ and $b = 7 x y$
$(9 x - 7 x y)^{2} = (9 x)^{2} - 2.9 x .7 x y + (7 x y)^{2}$ [using the identity, $(a - b)^{2} = a^{2} - 2 a b + b^{2}$ ]
$= 81 x^{2} - 126 x^{2} y + 49 x^{2} y^{2} = 81 x^{2} + 49 x^{2} y^{2} - 126 x^{2} y$

Question 18Square of 9x−7xy isa 81x2+49x2y2b 81x2−49x2y

Right Answer is:

SOLUTION

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