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Contents
Ratio for General Angles 1 2
Ratio for Complementary Angles
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Trigonometric Ratio of General Angles By using a calculator, we can only find acute angles when given the ratios. Let's say I press sin-1 0.5. I'll get 30. But do you know that when I press sin 150, I'll get 0.5 as well? Thus, we must first find a relationship between the ratios for such angles and a corresponding acute angle. Take note of the signs of the trigonometric ratios.
1st
Quadrant
These definitions agree with those you have already used in dealing with right-angled triangle.
2nd Quadrant
When the angle lies in the third quadrant, both components x and y are negative. a = 180° - q .
In this quadrant, the x component is positive, the y component is negative. a = 360° - q.
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We define the trigonometric ratios as follows:
