Solve 1/2sqrt{2+sqrt{5}}

$$\frac { 1 } { 2 \sqrt { 2 } + \sqrt { 5 } }$$

Evaluate

$$\frac{2\sqrt{2}-\sqrt{5}}{3}\approx 0.197453049$$

Solution Steps

Rationalize the denominator of \frac{1}{2\sqrt{2}+\sqrt{5}} by multiplying numerator and denominator by 2\sqrt{2}-\sqrt{5}.

$$\frac{2\sqrt{2}-\sqrt{5}}{\left(2\sqrt{2}+\sqrt{5}\right)\left(2\sqrt{2}-\sqrt{5}\right)}$$

Consider \left(2\sqrt{2}+\sqrt{5}\right)\left(2\sqrt{2}-\sqrt{5}\right). Multiplication can be transformed into difference of squares using the rule: \left(a-b\right)\left(a+b\right)=a^{2}-b^{2}.

$$\frac{2\sqrt{2}-\sqrt{5}}{\left(2\sqrt{2}\right)^{2}-\left(\sqrt{5}\right)^{2}}$$

Expand \left(2\sqrt{2}\right)^{2}.

$$\frac{2\sqrt{2}-\sqrt{5}}{2^{2}\left(\sqrt{2}\right)^{2}-\left(\sqrt{5}\right)^{2}}$$

Calculate 2 to the power of 2 and get 4.

$$\frac{2\sqrt{2}-\sqrt{5}}{4\left(\sqrt{2}\right)^{2}-\left(\sqrt{5}\right)^{2}}$$

The square of \sqrt{2} is 2.

$$\frac{2\sqrt{2}-\sqrt{5}}{4\times 2-\left(\sqrt{5}\right)^{2}}$$

Multiply 4 and 2 to get 8.

$$\frac{2\sqrt{2}-\sqrt{5}}{8-\left(\sqrt{5}\right)^{2}}$$

The square of \sqrt{5} is 5.

$$\frac{2\sqrt{2}-\sqrt{5}}{8-5}$$

Subtract 5 from 8 to get 3.

$$\frac{2\sqrt{2}-\sqrt{5}}{3}$$