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How to visualise sin, cos or tan for x>90?
While its height/perpendicular and so on for a rt. angled triangle it becomes difficult to visualise for say Sin(pi+x)? Suddenly got confused trying to explain to my sons.
The quadrants I understand, what I need to know is am I rotating the same right angled triangle?
1 Answer
- AnthonyLv 79 years agoFavorite Answer
Think of 180 degrees (pi radians) as 2 right angles back to back. Then think of 360 degrees (2pi radians) as 4 right angles or four quadrants..
Whatever the angle, say 120, think of it as 180-120 = 60 in the secon quadrant. 210 would be 30 in the third quadrant, 330 would be 30 in the fourth quadrant and so on.
Starting due east = 0 and due north = 90 degrees, sin,tan and cos of the angle is positive.
From due north to due west, 90 to 180, only sin is positive.tan and cos are negative.
From due west to due south, 180 to 270, tan is positive, sin and cos are negative.
From due south to due west, 270 to 360 degrees, cos is positive, tan and sin are negative.
