Solve 4/y^2-25+5/y^2-5y

$$\frac { 4 } { y ^ { 2 } - 25 } + \frac { 5 } { y ^ { 2 } - 5 y }$$

Evaluate

$$\frac{9y+25}{y\left(y^{2}-25\right)}$$

Short Solution Steps

Factor y^{2}-25. Factor y^{2}-5y.

$$\frac{4}{\left(y-5\right)\left(y+5\right)}+\frac{5}{y\left(y-5\right)}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(y-5\right)\left(y+5\right) and y\left(y-5\right) is y\left(y-5\right)\left(y+5\right). Multiply \frac{4}{\left(y-5\right)\left(y+5\right)} times \frac{y}{y}. Multiply \frac{5}{y\left(y-5\right)} times \frac{y+5}{y+5}.

$$\frac{4y}{y\left(y-5\right)\left(y+5\right)}+\frac{5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)}$$

Since \frac{4y}{y\left(y-5\right)\left(y+5\right)} and \frac{5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)} have the same denominator, add them by adding their numerators.

$$\frac{4y+5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)}$$

Do the multiplications in 4y+5\left(y+5\right).

$$\frac{4y+5y+25}{y\left(y-5\right)\left(y+5\right)}$$

Combine like terms in 4y+5y+25.

$$\frac{9y+25}{y\left(y-5\right)\left(y+5\right)}$$

Expand y\left(y-5\right)\left(y+5\right).

$$\frac{9y+25}{y^{3}-25y}$$

Differentiate w.r.t. y

$$\frac{625-75y^{2}-18y^{3}}{\left(y\left(y^{2}-25\right)\right)^{2}}$$

Steps Using Derivative Rule for Quotient

Factor y^{2}-25. Factor y^{2}-5y.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{4}{\left(y-5\right)\left(y+5\right)}+\frac{5}{y\left(y-5\right)})$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(y-5\right)\left(y+5\right) and y\left(y-5\right) is y\left(y-5\right)\left(y+5\right). Multiply \frac{4}{\left(y-5\right)\left(y+5\right)} times \frac{y}{y}. Multiply \frac{5}{y\left(y-5\right)} times \frac{y+5}{y+5}.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{4y}{y\left(y-5\right)\left(y+5\right)}+\frac{5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)})$$

Since \frac{4y}{y\left(y-5\right)\left(y+5\right)} and \frac{5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)} have the same denominator, add them by adding their numerators.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{4y+5\left(y+5\right)}{y\left(y-5\right)\left(y+5\right)})$$

Do the multiplications in 4y+5\left(y+5\right).

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{4y+5y+25}{y\left(y-5\right)\left(y+5\right)})$$

Combine like terms in 4y+5y+25.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{9y+25}{y\left(y-5\right)\left(y+5\right)})$$

Use the distributive property to multiply y by y-5.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{9y+25}{\left(y^{2}-5y\right)\left(y+5\right)})$$

Use the distributive property to multiply y^{2}-5y by y+5 and combine like terms.

$$\frac{\mathrm{d}}{\mathrm{d}y}(\frac{9y+25}{y^{3}-25y})$$

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.

$$\frac{\left(y^{3}-25y^{1}\right)\frac{\mathrm{d}}{\mathrm{d}y}(9y^{1}+25)-\left(9y^{1}+25\right)\frac{\mathrm{d}}{\mathrm{d}y}(y^{3}-25y^{1})}{\left(y^{3}-25y^{1}\right)^{2}}$$

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}.

$$\frac{\left(y^{3}-25y^{1}\right)\times 9y^{1-1}-\left(9y^{1}+25\right)\left(3y^{3-1}-25y^{1-1}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

Simplify.

$$\frac{\left(y^{3}-25y^{1}\right)\times 9y^{0}-\left(9y^{1}+25\right)\left(3y^{2}-25y^{0}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

Multiply y^{3}-25y^{1} times 9y^{0}.

$$\frac{y^{3}\times 9y^{0}-25y^{1}\times 9y^{0}-\left(9y^{1}+25\right)\left(3y^{2}-25y^{0}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

Multiply 9y^{1}+25 times 3y^{2}-25y^{0}.

$$\frac{y^{3}\times 9y^{0}-25y^{1}\times 9y^{0}-\left(9y^{1}\times 3y^{2}+9y^{1}\left(-25\right)y^{0}+25\times 3y^{2}+25\left(-25\right)y^{0}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

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

$$\frac{9y^{3}-25\times 9y^{1}-\left(9\times 3y^{1+2}+9\left(-25\right)y^{1}+25\times 3y^{2}+25\left(-25\right)y^{0}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

Simplify.

$$\frac{9y^{3}-225y^{1}-\left(27y^{3}-225y^{1}+75y^{2}-625y^{0}\right)}{\left(y^{3}-25y^{1}\right)^{2}}$$

Combine like terms.

$$\frac{-18y^{3}-9y^{2}+625y^{0}}{\left(y^{3}-25y^{1}\right)^{2}}$$

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

$$\frac{-18y^{3}-9y^{2}+625y^{0}}{\left(y^{3}-25y\right)^{2}}$$

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

$$\frac{-18y^{3}-9y^{2}+625\times 1}{\left(y^{3}-25y\right)^{2}}$$

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

$$\frac{-18y^{3}-9y^{2}+625}{\left(y^{3}-25y\right)^{2}}$$