# If X = 3 and Y = − 1, Find the Values of the Following Using in Identify: ( X Y − Y 3 ) X 2 16 + X Y 12 + Y 2 9 - Mathematics

If x = 3 and y = − 1, find the values of the following using in identify:

$\left( \frac{x}{y} - \frac{y}{3} \right) \frac{x^2}{16} + \frac{xy}{12} + \frac{y^2}{9}$

#### Solution

In the given problem, we have to find the value of equation using identity

Given $\left( \frac{x}{y} - \frac{y}{3} \right) \frac{x^2}{16} + \frac{xy}{12} + \frac{y^2}{9}$

We shall use the identity  (a-b) (a^3 + ab + b^2) = a^3 - b^3

We can rearrange the (x/4 - y/3) (x^2/16 + (xy)/12 + y^2/9)as

 =(x/4 - y/3) ((x/4)^2 + (y/3)^2 + (x/4)(y/3))

 = (x/4)^3 - (y/3)^3

$= \left( \frac{x}{4} \right) \times \left( \frac{x}{4} \right) \times \left( \frac{x}{4} \right) - \left( \frac{y}{3} \right) \times \left( \frac{y}{3} \right) \times \left( \frac{y}{3} \right)$

$= \frac{x^3}{64} - \frac{y^3}{27}$

Now substituting the value x=3, in  x^3/64 - y^3/27we get,

= x^3/64 - y^3/27

= (3)^3/64 - (-1)^3/27

 = 27/64 + 1/27

Taking Least common multiple, we get

 =(27 xx 27)/(64 xx 27) + (1 xx 64)/(27 xx 64)

=729/1728 + 64 /1728

 =(729 + 64)/1728

 = 793/1728

Hence the Product value of (x/4 - y/3)(x^2/16 + (xy)/12 + y^2/9)is  = 793/1728.

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#### APPEARS IN

RD Sharma Mathematics for Class 9
Chapter 4 Algebraic Identities
Exercise 4.4 | Q 2.4 | Page 24