Solve 13/x^2-225+11/x-15-7/x+15

$$\frac { 13 } { x ^ { 2 } - 225 } + \frac { 11 } { x - 15 } - \frac { 7 } { x + 15 }$$

Evaluate

$$\frac{4x+283}{x^{2}-225}$$

Short Solution Steps

Factor x^{2}-225.

$$\frac{13}{\left(x-15\right)\left(x+15\right)}+\frac{11}{x-15}-\frac{7}{x+15}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-15\right)\left(x+15\right) and x-15 is \left(x-15\right)\left(x+15\right). Multiply \frac{11}{x-15} times \frac{x+15}{x+15}.

$$\frac{13}{\left(x-15\right)\left(x+15\right)}+\frac{11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15}$$

Since \frac{13}{\left(x-15\right)\left(x+15\right)} and \frac{11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)} have the same denominator, add them by adding their numerators.

$$\frac{13+11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15}$$

Do the multiplications in 13+11\left(x+15\right).

$$\frac{13+11x+165}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15}$$

Combine like terms in 13+11x+165.

$$\frac{178+11x}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-15\right)\left(x+15\right) and x+15 is \left(x-15\right)\left(x+15\right). Multiply \frac{7}{x+15} times \frac{x-15}{x-15}.

$$\frac{178+11x}{\left(x-15\right)\left(x+15\right)}-\frac{7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)}$$

Since \frac{178+11x}{\left(x-15\right)\left(x+15\right)} and \frac{7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)} have the same denominator, subtract them by subtracting their numerators.

$$\frac{178+11x-7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)}$$

Do the multiplications in 178+11x-7\left(x-15\right).

$$\frac{178+11x-7x+105}{\left(x-15\right)\left(x+15\right)}$$

Combine like terms in 178+11x-7x+105.

$$\frac{283+4x}{\left(x-15\right)\left(x+15\right)}$$

Expand \left(x-15\right)\left(x+15\right).

$$\frac{283+4x}{x^{2}-225}$$

Differentiate w.r.t. x

$$-\frac{2\left(2x^{2}+283x+450\right)}{\left(x^{2}-225\right)^{2}}$$

Steps Using Derivative Rule for Quotient

Factor x^{2}-225.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{13}{\left(x-15\right)\left(x+15\right)}+\frac{11}{x-15}-\frac{7}{x+15})$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-15\right)\left(x+15\right) and x-15 is \left(x-15\right)\left(x+15\right). Multiply \frac{11}{x-15} times \frac{x+15}{x+15}.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{13}{\left(x-15\right)\left(x+15\right)}+\frac{11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15})$$

Since \frac{13}{\left(x-15\right)\left(x+15\right)} and \frac{11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)} have the same denominator, add them by adding their numerators.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{13+11\left(x+15\right)}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15})$$

Do the multiplications in 13+11\left(x+15\right).

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{13+11x+165}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15})$$

Combine like terms in 13+11x+165.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{178+11x}{\left(x-15\right)\left(x+15\right)}-\frac{7}{x+15})$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(x-15\right)\left(x+15\right) and x+15 is \left(x-15\right)\left(x+15\right). Multiply \frac{7}{x+15} times \frac{x-15}{x-15}.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{178+11x}{\left(x-15\right)\left(x+15\right)}-\frac{7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)})$$

Since \frac{178+11x}{\left(x-15\right)\left(x+15\right)} and \frac{7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)} have the same denominator, subtract them by subtracting their numerators.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{178+11x-7\left(x-15\right)}{\left(x-15\right)\left(x+15\right)})$$

Do the multiplications in 178+11x-7\left(x-15\right).

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{178+11x-7x+105}{\left(x-15\right)\left(x+15\right)})$$

Combine like terms in 178+11x-7x+105.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{283+4x}{\left(x-15\right)\left(x+15\right)})$$

Consider \left(x-15\right)\left(x+15\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 15.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{283+4x}{x^{2}-225})$$

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.

$$\frac{\left(x^{2}-225\right)\frac{\mathrm{d}}{\mathrm{d}x}(4x^{1}+283)-\left(4x^{1}+283\right)\frac{\mathrm{d}}{\mathrm{d}x}(x^{2}-225)}{\left(x^{2}-225\right)^{2}}$$

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}.

$$\frac{\left(x^{2}-225\right)\times 4x^{1-1}-\left(4x^{1}+283\right)\times 2x^{2-1}}{\left(x^{2}-225\right)^{2}}$$

Do the arithmetic.

$$\frac{\left(x^{2}-225\right)\times 4x^{0}-\left(4x^{1}+283\right)\times 2x^{1}}{\left(x^{2}-225\right)^{2}}$$

Expand using distributive property.

$$\frac{x^{2}\times 4x^{0}-225\times 4x^{0}-\left(4x^{1}\times 2x^{1}+283\times 2x^{1}\right)}{\left(x^{2}-225\right)^{2}}$$

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

$$\frac{4x^{2}-225\times 4x^{0}-\left(4\times 2x^{1+1}+283\times 2x^{1}\right)}{\left(x^{2}-225\right)^{2}}$$

Do the arithmetic.

$$\frac{4x^{2}-900x^{0}-\left(8x^{2}+566x^{1}\right)}{\left(x^{2}-225\right)^{2}}$$

Remove unnecessary parentheses.

$$\frac{4x^{2}-900x^{0}-8x^{2}-566x^{1}}{\left(x^{2}-225\right)^{2}}$$

Combine like terms.

$$\frac{\left(4-8\right)x^{2}-900x^{0}-566x^{1}}{\left(x^{2}-225\right)^{2}}$$

Subtract 8 from 4.

$$\frac{-4x^{2}-900x^{0}-566x^{1}}{\left(x^{2}-225\right)^{2}}$$

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

$$\frac{-4x^{2}-900x^{0}-566x}{\left(x^{2}-225\right)^{2}}$$

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

$$\frac{-4x^{2}-900-566x}{\left(x^{2}-225\right)^{2}}$$