Question

Find the exact value by using a half angle identity.tan 75°

Answer 1

The trigonometric function is given as

$\tan 75^{\circ}$

Apply the half angle identity to find the value of tan 75 ,

$\tan (\frac{u}{2})=\frac{\sin u}{1+\cos u}$

Here,

$\tan (\frac{150^{\circ}}{2})=\frac{\sin150^{\circ}}{1+cos150^{\circ}}$$\tan (75^{\circ})=\frac{\frac{1}{2}}{1-\frac{\sqrt[]{3}}{2}}=\frac{\frac{1}{2}}{\frac{2-\sqrt[]{3}}{2}}^{}$$\tan 75^{\circ}=\frac{1}{2-\sqrt[]{3}}$

Now rationalize the function.

$\tan 75^{\circ}=\frac{1}{2-\sqrt[]{3}}\times\frac{2+\sqrt[]{3}}{2+\sqrt[]{3}}=\frac{2+\sqrt[]{3}}{4-3}=\frac{2+\sqrt[]{3}}{1}$

Again simplify the trigonometric function,

$\tan 75^{\circ}=2+1.732=3.732$

Hence the answer is 3.732.