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I should have asked this question 6 months ago, when I learned this.

When using the quadrant diagram, how is it say for angle of 120 degrees, you can use 60 degrees to find trig ratios?

Like in this image - here

user376253
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1 Answers1

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You have

$120$ degrees$=90 +30$ or

$=\frac{\pi}{2}+\frac{\pi}{6}$.

we use following formulas:

$cos(a+\frac{\pi}{2})=-sin(a)$

$sin(a+\frac{\pi}{2})=cos(a)$.

hamam_Abdallah
  • 62,951