Solve 4/2r+5+3/5r-2

$$\frac { 4 } { 2 r + 5 } + \frac { 3 } { 5 r - 2 }$$

Evaluate

$$\frac{26r+7}{\left(5r-2\right)\left(2r+5\right)}$$

Short Solution Steps

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of 2r+5 and 5r-2 is \left(5r-2\right)\left(2r+5\right). Multiply \frac{4}{2r+5} times \frac{5r-2}{5r-2}. Multiply \frac{3}{5r-2} times \frac{2r+5}{2r+5}.

$$\frac{4\left(5r-2\right)}{\left(5r-2\right)\left(2r+5\right)}+\frac{3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)}$$

Since \frac{4\left(5r-2\right)}{\left(5r-2\right)\left(2r+5\right)} and \frac{3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)} have the same denominator, add them by adding their numerators.

$$\frac{4\left(5r-2\right)+3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)}$$

Do the multiplications in 4\left(5r-2\right)+3\left(2r+5\right).

$$\frac{20r-8+6r+15}{\left(5r-2\right)\left(2r+5\right)}$$

Combine like terms in 20r-8+6r+15.

$$\frac{26r+7}{\left(5r-2\right)\left(2r+5\right)}$$

Expand \left(5r-2\right)\left(2r+5\right).

$$\frac{26r+7}{10r^{2}+21r-10}$$

Differentiate w.r.t. r

$$-\frac{260r^{2}+140r+407}{\left(\left(5r-2\right)\left(2r+5\right)\right)^{2}}$$

Steps Using Derivative Rule for Quotient

To add or subtract expressions, expand them to make their denominators the same. Least common multiple of 2r+5 and 5r-2 is \left(5r-2\right)\left(2r+5\right). Multiply \frac{4}{2r+5} times \frac{5r-2}{5r-2}. Multiply \frac{3}{5r-2} times \frac{2r+5}{2r+5}.

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{4\left(5r-2\right)}{\left(5r-2\right)\left(2r+5\right)}+\frac{3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)})$$

Since \frac{4\left(5r-2\right)}{\left(5r-2\right)\left(2r+5\right)} and \frac{3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)} have the same denominator, add them by adding their numerators.

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{4\left(5r-2\right)+3\left(2r+5\right)}{\left(5r-2\right)\left(2r+5\right)})$$

Do the multiplications in 4\left(5r-2\right)+3\left(2r+5\right).

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{20r-8+6r+15}{\left(5r-2\right)\left(2r+5\right)})$$

Combine like terms in 20r-8+6r+15.

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{26r+7}{\left(5r-2\right)\left(2r+5\right)})$$

Apply the distributive property by multiplying each term of 5r-2 by each term of 2r+5.

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{26r+7}{10r^{2}+25r-4r-10})$$

Combine 25r and -4r to get 21r.

$$\frac{\mathrm{d}}{\mathrm{d}r}(\frac{26r+7}{10r^{2}+21r-10})$$

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.

$$\frac{\left(10r^{2}+21r^{1}-10\right)\frac{\mathrm{d}}{\mathrm{d}r}(26r^{1}+7)-\left(26r^{1}+7\right)\frac{\mathrm{d}}{\mathrm{d}r}(10r^{2}+21r^{1}-10)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

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}.

$$\frac{\left(10r^{2}+21r^{1}-10\right)\times 26r^{1-1}-\left(26r^{1}+7\right)\left(2\times 10r^{2-1}+21r^{1-1}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

Simplify.

$$\frac{\left(10r^{2}+21r^{1}-10\right)\times 26r^{0}-\left(26r^{1}+7\right)\left(20r^{1}+21r^{0}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

Multiply 10r^{2}+21r^{1}-10 times 26r^{0}.

$$\frac{10r^{2}\times 26r^{0}+21r^{1}\times 26r^{0}-10\times 26r^{0}-\left(26r^{1}+7\right)\left(20r^{1}+21r^{0}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

Multiply 26r^{1}+7 times 20r^{1}+21r^{0}.

$$\frac{10r^{2}\times 26r^{0}+21r^{1}\times 26r^{0}-10\times 26r^{0}-\left(26r^{1}\times 20r^{1}+26r^{1}\times 21r^{0}+7\times 20r^{1}+7\times 21r^{0}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

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

$$\frac{10\times 26r^{2}+21\times 26r^{1}-10\times 26r^{0}-\left(26\times 20r^{1+1}+26\times 21r^{1}+7\times 20r^{1}+7\times 21r^{0}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

Simplify.

$$\frac{260r^{2}+546r^{1}-260r^{0}-\left(520r^{2}+546r^{1}+140r^{1}+147r^{0}\right)}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

Combine like terms.

$$\frac{-260r^{2}-140r^{1}-407r^{0}}{\left(10r^{2}+21r^{1}-10\right)^{2}}$$

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

$$\frac{-260r^{2}-140r-407r^{0}}{\left(10r^{2}+21r-10\right)^{2}}$$

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

$$\frac{-260r^{2}-140r-407}{\left(10r^{2}+21r-10\right)^{2}}$$