Solve x/x-4-3/16-x^2

$$\frac { x } { x - 4 } - \frac { 3 } { 16 - x ^ { 2 } }$$

Evaluate

$$\frac{\left(x+1\right)\left(x+3\right)}{x^{2}-16}$$

Short Solution Steps

Factor 16-x^{2}.

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

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of x-4 and \left(x-4\right)\left(-x-4\right) is \left(x-4\right)\left(-x-4\right). Multiply \frac{x}{x-4} times \frac{-x-4}{-x-4}.

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

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

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

Do the multiplications in x\left(-x-4\right)-3.

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

Expand \left(x-4\right)\left(-x-4\right).

$$\frac{-x^{2}-4x-3}{-x^{2}+16}$$

Differentiate w.r.t. x

$$-\frac{2\left(2x^{2}+19x+32\right)}{\left(x^{2}-16\right)^{2}}$$

Steps Using Derivative Rule for Quotient

Factor 16-x^{2}.

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

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of x-4 and \left(x-4\right)\left(-x-4\right) is \left(x-4\right)\left(-x-4\right). Multiply \frac{x}{x-4} times \frac{-x-4}{-x-4}.

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

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

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

Do the multiplications in x\left(-x-4\right)-3.

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

Use the distributive property to multiply x-4 by -x-4 and combine like terms.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{-x^{2}-4x-3}{-x^{2}+16})$$

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.

$$\frac{\left(-x^{2}+16\right)\frac{\mathrm{d}}{\mathrm{d}x}(-x^{2}-4x^{1}-3)-\left(-x^{2}-4x^{1}-3\right)\frac{\mathrm{d}}{\mathrm{d}x}(-x^{2}+16)}{\left(-x^{2}+16\right)^{2}}$$

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}.

$$\frac{\left(-x^{2}+16\right)\left(2\left(-1\right)x^{2-1}-4x^{1-1}\right)-\left(-x^{2}-4x^{1}-3\right)\times 2\left(-1\right)x^{2-1}}{\left(-x^{2}+16\right)^{2}}$$

Simplify.

$$\frac{\left(-x^{2}+16\right)\left(-2x^{1}-4x^{0}\right)-\left(-x^{2}-4x^{1}-3\right)\left(-2\right)x^{1}}{\left(-x^{2}+16\right)^{2}}$$

Multiply -x^{2}+16 times -2x^{1}-4x^{0}.

$$\frac{-x^{2}\left(-2\right)x^{1}-x^{2}\left(-4\right)x^{0}+16\left(-2\right)x^{1}+16\left(-4\right)x^{0}-\left(-x^{2}-4x^{1}-3\right)\left(-2\right)x^{1}}{\left(-x^{2}+16\right)^{2}}$$

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

$$\frac{-x^{2}\left(-2\right)x^{1}-x^{2}\left(-4\right)x^{0}+16\left(-2\right)x^{1}+16\left(-4\right)x^{0}-\left(-x^{2}\left(-2\right)x^{1}-4x^{1}\left(-2\right)x^{1}-3\left(-2\right)x^{1}\right)}{\left(-x^{2}+16\right)^{2}}$$

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

$$\frac{-\left(-2\right)x^{2+1}-\left(-4x^{2}\right)+16\left(-2\right)x^{1}+16\left(-4\right)x^{0}-\left(-\left(-2\right)x^{2+1}-4\left(-2\right)x^{1+1}-3\left(-2\right)x^{1}\right)}{\left(-x^{2}+16\right)^{2}}$$

Simplify.

$$\frac{2x^{3}+4x^{2}-32x^{1}-64x^{0}-\left(2x^{3}+8x^{2}+6x^{1}\right)}{\left(-x^{2}+16\right)^{2}}$$

Combine like terms.

$$\frac{-4x^{2}-38x^{1}-64x^{0}}{\left(-x^{2}+16\right)^{2}}$$

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

$$\frac{-4x^{2}-38x-64x^{0}}{\left(-x^{2}+16\right)^{2}}$$

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

$$\frac{-4x^{2}-38x-64}{\left(-x^{2}+16\right)^{2}}$$