Solve 9x/x-85/x-4

$$\frac{ 9x }{ x-8 } \frac{ 5 }{ x-4 }$$

Evaluate

$$\frac{45x}{\left(x-8\right)\left(x-4\right)}$$

Short Solution Steps

Multiply \frac{9x}{x-8} times \frac{5}{x-4} by multiplying numerator times numerator and denominator times denominator.

$$\frac{9x\times 5}{\left(x-8\right)\left(x-4\right)}$$

Multiply 9 and 5 to get 45.

$$\frac{45x}{\left(x-8\right)\left(x-4\right)}$$

Apply the distributive property by multiplying each term of x-8 by each term of x-4.

$$\frac{45x}{x^{2}-4x-8x+32}$$

Combine -4x and -8x to get -12x.

$$\frac{45x}{x^{2}-12x+32}$$

Differentiate w.r.t. x

$$\frac{45\left(32-x^{2}\right)}{\left(\left(x-8\right)\left(x-4\right)\right)^{2}}$$

Steps Using Derivative Rule for Quotient

Multiply \frac{9x}{x-8} times \frac{5}{x-4} by multiplying numerator times numerator and denominator times denominator.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{9x\times 5}{\left(x-8\right)\left(x-4\right)})$$

Multiply 9 and 5 to get 45.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{45x}{\left(x-8\right)\left(x-4\right)})$$

Apply the distributive property by multiplying each term of x-8 by each term of x-4.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{45x}{x^{2}-4x-8x+32})$$

Combine -4x and -8x to get -12x.

$$\frac{\mathrm{d}}{\mathrm{d}x}(\frac{45x}{x^{2}-12x+32})$$

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.

$$\frac{\left(x^{2}-12x^{1}+32\right)\frac{\mathrm{d}}{\mathrm{d}x}(45x^{1})-45x^{1}\frac{\mathrm{d}}{\mathrm{d}x}(x^{2}-12x^{1}+32)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

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}.

$$\frac{\left(x^{2}-12x^{1}+32\right)\times 45x^{1-1}-45x^{1}\left(2x^{2-1}-12x^{1-1}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

Simplify.

$$\frac{\left(x^{2}-12x^{1}+32\right)\times 45x^{0}-45x^{1}\left(2x^{1}-12x^{0}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

Multiply x^{2}-12x^{1}+32 times 45x^{0}.

$$\frac{x^{2}\times 45x^{0}-12x^{1}\times 45x^{0}+32\times 45x^{0}-45x^{1}\left(2x^{1}-12x^{0}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

Multiply 45x^{1} times 2x^{1}-12x^{0}.

$$\frac{x^{2}\times 45x^{0}-12x^{1}\times 45x^{0}+32\times 45x^{0}-\left(45x^{1}\times 2x^{1}+45x^{1}\left(-12\right)x^{0}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

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

$$\frac{45x^{2}-12\times 45x^{1}+32\times 45x^{0}-\left(45\times 2x^{1+1}+45\left(-12\right)x^{1}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

Simplify.

$$\frac{45x^{2}-540x^{1}+1440x^{0}-\left(90x^{2}-540x^{1}\right)}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

Combine like terms.

$$\frac{-45x^{2}+1440x^{0}}{\left(x^{2}-12x^{1}+32\right)^{2}}$$

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

$$\frac{-45x^{2}+1440x^{0}}{\left(x^{2}-12x+32\right)^{2}}$$

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

$$\frac{-45x^{2}+1440\times 1}{\left(x^{2}-12x+32\right)^{2}}$$

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

$$\frac{-45x^{2}+1440}{\left(x^{2}-12x+32\right)^{2}}$$