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Question

If $3x + 2y = 10$ and $2xy = 3$, then find the positive value of $3x - 2y$.

The correct answer is
8

Solving for the Positive Value of 3x - 2y

We are given two equations:

  • Equation 1: \(3x + 2y = 10\)
  • Equation 2: \(2xy = 3\)

Our goal is to find the positive value of the expression \(3x - 2y\).

Using Algebraic Identities

We can use the algebraic identity that relates the square of a sum and the square of a difference:

$ (a - b)^2 = (a + b)^2 - 4ab $

Let \(a = 3x\) and \(b = 2y\). Substituting these into the identity, we get:

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

Simplify the term \(4(3x)(2y)\):

$ 4(3x)(2y) = 24xy $

We are given \(2xy = 3\). To find \(24xy\), we can multiply the given value by 12:

$ 24xy = 12 \times (2xy) = 12 \times 3 = 36 $

Now substitute the known values into the expanded identity:

  • \( (3x + 2y)^2 = (10)^2 = 100 \)
  • \( 24xy = 36 \)

So, the equation becomes:

$ (3x - 2y)^2 = 100 - 36 $

$ (3x - 2y)^2 = 64 $

Determining the Positive Value

To find the value of \(3x - 2y\), we take the square root of both sides:

$ 3x - 2y = \pm \sqrt{64} $

$ 3x - 2y = \pm 8 $

The question specifically asks for the positive value.

Therefore, the positive value of \(3x - 2y\) is 8.

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Important Questions from Identities

  1. The coefficient of y in the expansion of (2y – 5) 3, is:

  2. If x + y = 2 and \(\frac{1}{x}+\frac{1}{y}=\frac{18}{5}\) , then the value of (x 3+ y 3) is:

  3. If x - y = 11 and \(\rm \frac{1}{x} - \frac{1}{y} = \frac{11}{24}\)  then the value of x 3 - y 3 + x 2y 2 ?

  4. If 2x 2- 8x - 1 = 0, then what is the value of \(\rm 8x^3 - \frac{1}{x^3}\) ?

  5. If \(\rm x+ \frac{1}{x} = 4,\)  then the value of  \(\rm x^5 + \frac{1}{x^5}\)  is:

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