Solve (-r^4/64r^7)^frac{2{3}}

$$( \frac { - r ^ { 4 } } { 64 r ^ { 7 } } ) ^ { \frac { 2 } { 3 } }$$

Evaluate

$$\frac{1}{16r^{2}}$$

Solution Steps

To raise \frac{-r^{4}}{64r^{7}} to a power, raise both numerator and denominator to the power and then divide.

$$\frac{\left(-r^{4}\right)^{\frac{2}{3}}}{\left(64r^{7}\right)^{\frac{2}{3}}}$$

Expand \left(64r^{7}\right)^{\frac{2}{3}}.

$$\frac{\left(-r^{4}\right)^{\frac{2}{3}}}{64^{\frac{2}{3}}\left(r^{7}\right)^{\frac{2}{3}}}$$

To raise a power to another power, multiply the exponents. Multiply 7 and \frac{2}{3} to get \frac{14}{3}.

$$\frac{\left(-r^{4}\right)^{\frac{2}{3}}}{64^{\frac{2}{3}}r^{\frac{14}{3}}}$$

Calculate 64 to the power of \frac{2}{3} and get 16.

$$\frac{\left(-r^{4}\right)^{\frac{2}{3}}}{16r^{\frac{14}{3}}}$$

Expand \left(-r^{4}\right)^{\frac{2}{3}}.

$$\frac{\left(-1\right)^{\frac{2}{3}}\left(r^{4}\right)^{\frac{2}{3}}}{16r^{\frac{14}{3}}}$$

To raise a power to another power, multiply the exponents. Multiply 4 and \frac{2}{3} to get \frac{8}{3}.

$$\frac{\left(-1\right)^{\frac{2}{3}}r^{\frac{8}{3}}}{16r^{\frac{14}{3}}}$$

Calculate -1 to the power of \frac{2}{3} and get 1.

$$\frac{1r^{\frac{8}{3}}}{16r^{\frac{14}{3}}}$$

Cancel out r^{\frac{8}{3}} in both numerator and denominator.

$$\frac{1}{16r^{2}}$$

Differentiate w.r.t. r

$$-\frac{1}{8r^{3}}$$

Steps Using Chain Rule

If F is the composition of two differentiable functions f\left(u\right) and u=g\left(x\right), that is, if F\left(x\right)=f\left(g\left(x\right)\right), then the derivative of F is the derivative of f with respect to u times the derivative of g with respect to x, that is, \frac{\mathrm{d}}{\mathrm{d}x}(F)\left(x\right)=\frac{\mathrm{d}}{\mathrm{d}x}(f)\left(g\left(x\right)\right)\frac{\mathrm{d}}{\mathrm{d}x}(g)\left(x\right).

$$\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{\frac{2}{3}-1}\frac{\mathrm{d}}{\mathrm{d}r}(\frac{-r^{4}}{64r^{7}})$$

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.

$$\frac{\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{\frac{2}{3}-1}\left(64r^{7}\frac{\mathrm{d}}{\mathrm{d}r}(-r^{4})-\left(-r^{4}\frac{\mathrm{d}}{\mathrm{d}r}(64r^{7})\right)\right)}{\left(64r^{7}\right)^{2}}$$

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}.

$$\frac{\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{\frac{2}{3}-1}\left(64r^{7}\times 4\left(-1\right)r^{4-1}-\left(-r^{4}\times 7\times 64r^{7-1}\right)\right)}{\left(64r^{7}\right)^{2}}$$

Multiply 64r^{7} times 4\left(-1\right)r^{4-1}.

$$\frac{\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{-\frac{1}{3}}\left(-256r^{7}r^{3}-\left(-r^{4}\times 7\times 64r^{7-1}\right)\right)}{\left(64r^{7}\right)^{2}}$$

Multiply -r^{4} times 7\times 64r^{7-1}.

$$\frac{\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{-\frac{1}{3}}\left(-256r^{10}-\left(-448r^{4}r^{6}\right)\right)}{\left(64r^{7}\right)^{2}}$$

Simplify.

$$\frac{\frac{2}{3}\times \left(\frac{-r^{4}}{64r^{7}}\right)^{-\frac{1}{3}}\left(-256r^{10}-\left(-448r^{10}\right)\right)}{\left(64r^{7}\right)^{2}}$$