Chapter 2 - Acute Angles and Right Triangles - Section 2.3 Finding Trigonometric Function Values Using a Calculator - 2.3 Exercises - Page 67: 67

$51^{\circ}; 231^{\circ}$

Using degree mode and inverse tangent function, we get $\theta=\tan^{-1}1.2348971=51^{\circ}$ Another possible value of $\theta$ can be found by using the identity $\tan(180^{\circ}+x)=\tan x$ $\implies \tan 51^{\circ}=\tan(180+51)^{\circ}=\tan 231^{\circ}$ $\implies\tan^{-1}1.2348971=51^{\circ}$ or $\tan^{-1}1.2348971=231^{\circ}$