Question

Find the reference angle for 120${}^o$.

• A. quadrant I, $\alpha ={45}^o$
• B. quadrant II, $\alpha ={60}^o$
• C. quadrant II, $\alpha ={50}^o$
• D. quadrant III, $\alpha ={55}^o$

Answer 1

Answer: (B)

quadrant II, $\alpha ={60}^o$

$I\to 0^o-{90}^{o}II\to {90}^o-{180}^{o}III\to {180}^o-{270}^{o}IV\to {270}^o-{360}^o$
Now, since, it is lying in the $II$ quadrant
${180}^o-{120}^o={60}^o$ is the reference angle
the $\text{reference angle}$ measures the closest angle of that terminal side to the x-axis.
Therefore, Answer is ${60}^o$