Math Problem Statement

if x=2-√3 then find (x²-1/x²)

Solution

Given that x=23x = 2 - \sqrt{3}, we need to find the value of x21x2x^2 - \frac{1}{x^2}.

Step 1: Find x2x^2

We begin by squaring both sides of the equation x=23x = 2 - \sqrt{3}.

x2=(23)2x^2 = (2 - \sqrt{3})^2

Using the identity (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2:

x2=222(2)(3)+(3)2x^2 = 2^2 - 2(2)(\sqrt{3}) + (\sqrt{3})^2 x2=443+3x^2 = 4 - 4\sqrt{3} + 3 x2=743x^2 = 7 - 4\sqrt{3}

Step 2: Find 1x\frac{1}{x}

Now, we need to compute 1x\frac{1}{x}. Since x=23x = 2 - \sqrt{3}, we rationalize the denominator by multiplying by the conjugate:

1x=123×2+32+3\frac{1}{x} = \frac{1}{2 - \sqrt{3}} \times \frac{2 + \sqrt{3}}{2 + \sqrt{3}} 1x=2+3(23)(2+3)\frac{1}{x} = \frac{2 + \sqrt{3}}{(2 - \sqrt{3})(2 + \sqrt{3})} Using the difference of squares:

1x=2+343\frac{1}{x} = \frac{2 + \sqrt{3}}{4 - 3} 1x=2+3\frac{1}{x} = 2 + \sqrt{3}

Step 3: Find 1x2\frac{1}{x^2}

Square 1x\frac{1}{x}:

1x2=(2+3)2\frac{1}{x^2} = (2 + \sqrt{3})^2 Using the same expansion formula:

1x2=22+2(2)(3)+(3)2\frac{1}{x^2} = 2^2 + 2(2)(\sqrt{3}) + (\sqrt{3})^2 1x2=4+43+3\frac{1}{x^2} = 4 + 4\sqrt{3} + 3 1x2=7+43\frac{1}{x^2} = 7 + 4\sqrt{3}

Step 4: Calculate x21x2x^2 - \frac{1}{x^2}

Now we subtract 1x2\frac{1}{x^2} from x2x^2:

x21x2=(743)(7+43)x^2 - \frac{1}{x^2} = (7 - 4\sqrt{3}) - (7 + 4\sqrt{3}) x21x2=774343x^2 - \frac{1}{x^2} = 7 - 7 - 4\sqrt{3} - 4\sqrt{3} x21x2=83x^2 - \frac{1}{x^2} = -8\sqrt{3}

Thus, the value of x21x2x^2 - \frac{1}{x^2} is 83-8\sqrt{3}.

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Here are 5 related questions for practice:

  1. If x=32x = 3 - \sqrt{2}, find x21x2x^2 - \frac{1}{x^2}.
  2. Simplify (ab)2(a - b)^2 and explain the process.
  3. What is the value of x41x4x^4 - \frac{1}{x^4} for x=23x = 2 - \sqrt{3}?
  4. Explain the process of rationalizing the denominator of 1ab\frac{1}{a - b}.
  5. What is the general formula for xn1xnx^n - \frac{1}{x^n} if x=abx = a - b?

Tip: When rationalizing a denominator, always multiply by the conjugate to eliminate square roots.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Rationalization
Radical Expressions

Formulas

(a - b)^2 = a^2 - 2ab + b^2
Difference of squares: (a - b)(a + b) = a^2 - b^2

Theorems

Rationalization of Denominator
Square of Binomial Theorem

Suitable Grade Level

Grades 10-12