Math Problem Statement

Evaluate the limit as x approaches a: lim (x -> a) [(sqrt(9 + 2x) - sqrt(3x)) / (sqrt(3a + x) - 2sqrt(x))]

Solution

This is a limit problem involving radicals:

limxa9+2x3x3a+x2x\lim_{x \to a} \frac{\sqrt{9+2x} - \sqrt{3x}}{\sqrt{3a+x} - 2\sqrt{x}}

To solve this, rationalize both the numerator and denominator separately by multiplying and dividing by their respective conjugates. Here's the process:

Step 1: Rationalize the numerator

The numerator is: 9+2x3x\sqrt{9+2x} - \sqrt{3x} Multiply and divide by its conjugate: 9+2x3x3a+x2x9+2x+3x9+2x+3x\frac{\sqrt{9+2x} - \sqrt{3x}}{\sqrt{3a+x} - 2\sqrt{x}} \cdot \frac{\sqrt{9+2x} + \sqrt{3x}}{\sqrt{9+2x} + \sqrt{3x}}

After simplification: Numerator becomes: (9+2x)(3x)9+2x+3x=9x9+2x+3x\text{Numerator becomes: } \frac{(9+2x) - (3x)}{\sqrt{9+2x} + \sqrt{3x}} = \frac{9 - x}{\sqrt{9+2x} + \sqrt{3x}}

Step 2: Rationalize the denominator

The denominator is: 3a+x2x\sqrt{3a+x} - 2\sqrt{x} Multiply and divide by its conjugate: 3a+x2x3a+x2x3a+x+2x3a+x+2x\frac{\sqrt{3a+x} - 2\sqrt{x}}{\sqrt{3a+x} - 2\sqrt{x}} \cdot \frac{\sqrt{3a+x} + 2\sqrt{x}}{\sqrt{3a+x} + 2\sqrt{x}}

After simplification: Denominator becomes: (3a+x)4x3a+x+2x=3a3x3a+x+2x\text{Denominator becomes: } \frac{(3a+x) - 4x}{\sqrt{3a+x} + 2\sqrt{x}} = \frac{3a - 3x}{\sqrt{3a+x} + 2\sqrt{x}}

Step 3: Substitute into the limit

Now the fraction becomes: limxa9x9+2x+3x3a3x3a+x+2x\lim_{x \to a} \frac{\frac{9 - x}{\sqrt{9+2x} + \sqrt{3x}}}{\frac{3a - 3x}{\sqrt{3a+x} + 2\sqrt{x}}}

This simplifies further to: limxa(9x)(3a+x+2x)(3a3x)(9+2x+3x)\lim_{x \to a} \frac{(9-x)(\sqrt{3a+x} + 2\sqrt{x})}{(3a-3x)(\sqrt{9+2x} + \sqrt{3x})}

Step 4: Substitute x=ax = a (if no indeterminate form arises)

After substituting x=ax = a: (9a)(3a+a+2a)(3a3a)(9+2a+3a)\frac{(9-a)(\sqrt{3a+a} + 2\sqrt{a})}{(3a-3a)(\sqrt{9+2a} + \sqrt{3a})}

The full expansion simplifies numerical simpl ax$$\lim_{x \to a}\ .Let's simplify this carefully:

We are solving: [ \lim_{x \to a} \frac{\sqrt{9+2x} - \sqrt{3x}}{\sqrt{3a+x} - 2\sqrt{x}}$$

Step 1: Analyze numerator

The numerator is: 9+2x3x\sqrt{9+2x} - \sqrt{3x} Multiply and divide by its conjugate: 9+2x3x9+2x+3x\frac{\sqrt{9+2x} - \sqrt{3x}}{\sqrt{9+2x} + \sqrt{3x}} This simplifies to: (9+2x)(3x)9+2x+3x=9x9+2x+3x\frac{(9+2x) - (3x)}{\sqrt{9+2x} + \sqrt{3x}} = \frac{9 - x}{\sqrt{9+2x} + \sqrt{3x}}

Step 2: Analyze denominator

The denominator is: 3a+x2x\sqrt{3a+x} - 2\sqrt{x} Multiply and divide by its conjugate: 3a+x2x3a+x+2x\frac{\sqrt{3a+x} - 2\sqrt{x}}{\sqrt{3a+x} + 2\sqrt{x}} This simplifies to: (3a+x)4x3a+x+2x=3a3x3a+x+2x\frac{(3a+x) - 4x}{\sqrt{3a+x} + 2\sqrt{x}} = \frac{3a - 3x}{\sqrt{3a+x} + 2\sqrt{x}}

Step 3: Combine numerator and denominator

The limit becomes: limxa9x9+2x+3x3a3x3a+x+2x\lim_{x \to a} \frac{\frac{9-x}{\sqrt{9+2x} + \sqrt{3x}}}{\frac{3a-3x}{\sqrt{3a+x} + 2\sqrt{x}}}

This simplifies further to: limxa(9x)(3a+x+2x)(3a3x)(9+2x+3x)\lim_{x \to a} \frac{(9-x)(\sqrt{3a+x} + 2\sqrt{x})}{(3a-3x)(\sqrt{9+2x} + \sqrt{3x})}

Step 4: Factorize and evaluate the limit

Observe that as xax \to a, the numerators and denominators approach non-zero values. Substitute x=ax = a to find the final result:

Substitute x=ax = a directly: (9a)(3a+a+2a)(3a3a)(9+2a+3a)\frac{(9-a)(\sqrt{3a+a} + 2\sqrt{a})}{(3a-3a)(\sqrt{9+2a} + \sqrt{3a})}

If indeterminate forms appear, further algebraic adjustments are necessary. Would you like more help refining this solution? Let me know!

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Math Problem Analysis

Mathematical Concepts

Limits
Rationalization
Radicals

Formulas

Difference of squares: (a - b)(a + b) = a^2 - b^2
Simplifying radicals: sqrt(a + b) * sqrt(a - b)

Theorems

Limit Laws

Suitable Grade Level

Grades 11-12