Solve 2mn/m^3+n^3+2m/m^2-n^2-1/m-n

$$\frac { 2 m n } { m ^ { 3 } + n ^ { 3 } } + \frac { 2 m } { m ^ { 2 } - n ^ { 2 } } - \frac { 1 } { m - n }$$

Evaluate

$$\frac{m^{2}+mn+n^{2}}{m^{3}+n^{3}}$$

Short Solution Steps

Factor m^{3}+n^{3}. Factor m^{2}-n^{2}.

$$\frac{2mn}{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}+\frac{2m}{\left(m+n\right)\left(m-n\right)}-\frac{1}{m-n}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(m+n\right)\left(m^{2}-mn+n^{2}\right) and \left(m+n\right)\left(m-n\right) is \left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right). Multiply \frac{2mn}{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)} times \frac{m-n}{m-n}. Multiply \frac{2m}{\left(m+n\right)\left(m-n\right)} times \frac{m^{2}-mn+n^{2}}{m^{2}-mn+n^{2}}.

$$\frac{2mn\left(m-n\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}+\frac{2m\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}-\frac{1}{m-n}$$

Since \frac{2mn\left(m-n\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)} and \frac{2m\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)} have the same denominator, add them by adding their numerators.

$$\frac{2mn\left(m-n\right)+2m\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}-\frac{1}{m-n}$$

Do the multiplications in 2mn\left(m-n\right)+2m\left(m^{2}-mn+n^{2}\right).

$$\frac{2m^{2}n-2mn^{2}+2m^{3}-2m^{2}n+2mn^{2}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}-\frac{1}{m-n}$$

Combine like terms in 2m^{2}n-2mn^{2}+2m^{3}-2m^{2}n+2mn^{2}.

$$\frac{2m^{3}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}-\frac{1}{m-n}$$

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of \left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right) and m-n is \left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right). Multiply \frac{1}{m-n} times \frac{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}.

$$\frac{2m^{3}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}-\frac{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}$$

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

$$\frac{2m^{3}-\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}$$

Do the multiplications in 2m^{3}-\left(m+n\right)\left(m^{2}-mn+n^{2}\right).

$$\frac{2m^{3}-m^{3}+m^{2}n-mn^{2}-nm^{2}+n^{2}m-n^{3}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}$$

Combine like terms in 2m^{3}-m^{3}+m^{2}n-mn^{2}-nm^{2}+n^{2}m-n^{3}.

$$\frac{m^{3}-n^{3}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}$$

Factor the expressions that are not already factored in \frac{m^{3}-n^{3}}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}.

$$\frac{\left(m-n\right)\left(m^{2}+mn+n^{2}\right)}{\left(m+n\right)\left(m-n\right)\left(m^{2}-mn+n^{2}\right)}$$

Cancel out m-n in both numerator and denominator.

$$\frac{m^{2}+mn+n^{2}}{\left(m+n\right)\left(m^{2}-mn+n^{2}\right)}$$

Expand \left(m+n\right)\left(m^{2}-mn+n^{2}\right).

$$\frac{m^{2}+mn+n^{2}}{m^{3}+n^{3}}$$

Differentiate w.r.t. m

$$\frac{-m^{4}+2mn^{3}+n^{4}-2nm^{3}-3\left(mn\right)^{2}}{\left(m^{3}+n^{3}\right)^{2}}$$