Solve 4x^2/x^2-9-3/x+3

$$\frac{ 4 { x }^{ 2 } }{ { x }^{ 2 } -9 } - \frac{ 3 }{ x+3 }$$

Evaluate

$$\frac{4x^{2}-3x+9}{x^{2}-9}$$

Short Solution Steps

Factor x^{2}-9.

$$\frac{4x^{2}}{\left(x-3\right)\left(x+3\right)}-\frac{3}{x+3}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-3\right)\left(x+3\right) and x+3 is \left(x-3\right)\left(x+3\right). Multiply \frac{3}{x+3} times \frac{x-3}{x-3}.

$$\frac{4x^{2}}{\left(x-3\right)\left(x+3\right)}-\frac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}$$

Since \frac{4x^{2}}{\left(x-3\right)\left(x+3\right)} and \frac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)} have the same denominator, subtract them by subtracting their numerators.

$$\frac{4x^{2}-3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}$$

Do the multiplications in 4x^{2}-3\left(x-3\right).

$$\frac{4x^{2}-3x+9}{\left(x-3\right)\left(x+3\right)}$$

Expand \left(x-3\right)\left(x+3\right).

$$\frac{4x^{2}-3x+9}{x^{2}-9}$$

Differentiate w.r.t. x

$$\frac{3\left(x^{2}-30x+9\right)}{\left(x^{2}-9\right)^{2}}$$

Steps Using Derivative Rule for Quotient

Factor x^{2}-9.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{4x^{2}}{\left(x-3\right)\left(x+3\right)}-\frac{3}{x+3})$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-3\right)\left(x+3\right) and x+3 is \left(x-3\right)\left(x+3\right). Multiply \frac{3}{x+3} times \frac{x-3}{x-3}.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{4x^{2}}{\left(x-3\right)\left(x+3\right)}-\frac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)})$$

Since \frac{4x^{2}}{\left(x-3\right)\left(x+3\right)} and \frac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)} have the same denominator, subtract them by subtracting their numerators.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{4x^{2}-3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)})$$

Do the multiplications in 4x^{2}-3\left(x-3\right).

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{4x^{2}-3x+9}{\left(x-3\right)\left(x+3\right)})$$

Consider \left(x-3\right)\left(x+3\right). Multiplication can be transformed into difference of squares using the rule: \left(a-b\right)\left(a+b\right)=a^{2}-b^{2}. Square 3.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{4x^{2}-3x+9}{x^{2}-9})$$

For any two differentiable functions, the derivative of the quotient of two functions is the denominator times the derivative of the numerator minus the numerator times the derivative of the denominator, all divided by the denominator squared.

$$\frac{\left(x^{2}-9\right)\frac{\mathrm{d}}{\mathrm{d}x}(4x^{2}-3x^{1}+9)-\left(4x^{2}-3x^{1}+9\right)\frac{\mathrm{d}}{\mathrm{d}x}(x^{2}-9)}{\left(x^{2}-9\right)^{2}}$$

The derivative of a polynomial is the sum of the derivatives of its terms. The derivative of a constant term is 0. The derivative of ax^{n} is nax^{n-1}.

$$\frac{\left(x^{2}-9\right)\left(2\times 4x^{2-1}-3x^{1-1}\right)-\left(4x^{2}-3x^{1}+9\right)\times 2x^{2-1}}{\left(x^{2}-9\right)^{2}}$$

Simplify.

$$\frac{\left(x^{2}-9\right)\left(8x^{1}-3x^{0}\right)-\left(4x^{2}-3x^{1}+9\right)\times 2x^{1}}{\left(x^{2}-9\right)^{2}}$$

Multiply x^{2}-9 times 8x^{1}-3x^{0}.

$$\frac{x^{2}\times 8x^{1}+x^{2}\left(-3\right)x^{0}-9\times 8x^{1}-9\left(-3\right)x^{0}-\left(4x^{2}-3x^{1}+9\right)\times 2x^{1}}{\left(x^{2}-9\right)^{2}}$$

Multiply 4x^{2}-3x^{1}+9 times 2x^{1}.

$$\frac{x^{2}\times 8x^{1}+x^{2}\left(-3\right)x^{0}-9\times 8x^{1}-9\left(-3\right)x^{0}-\left(4x^{2}\times 2x^{1}-3x^{1}\times 2x^{1}+9\times 2x^{1}\right)}{\left(x^{2}-9\right)^{2}}$$

To multiply powers of the same base, add their exponents.

$$\frac{8x^{2+1}-3x^{2}-9\times 8x^{1}-9\left(-3\right)x^{0}-\left(4\times 2x^{2+1}-3\times 2x^{1+1}+9\times 2x^{1}\right)}{\left(x^{2}-9\right)^{2}}$$

Simplify.

$$\frac{8x^{3}-3x^{2}-72x^{1}+27x^{0}-\left(8x^{3}-6x^{2}+18x^{1}\right)}{\left(x^{2}-9\right)^{2}}$$

Combine like terms.

$$\frac{3x^{2}-90x^{1}+27x^{0}}{\left(x^{2}-9\right)^{2}}$$

For any term t, t^{1}=t.

$$\frac{3x^{2}-90x+27x^{0}}{\left(x^{2}-9\right)^{2}}$$

For any term t except 0, t^{0}=1.

$$\frac{3x^{2}-90x+27\times 1}{\left(x^{2}-9\right)^{2}}$$

For any term t, t\times 1=t and 1t=t.

$$\frac{3x^{2}-90x+27}{\left(x^{2}-9\right)^{2}}$$