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Reference Angles
REFERENCE ANGLE : a positive acute angle made by the terminal side of an angle and the x­axis.
Quadrant I Quadrant IIQuadrant IIIQuadrant IV
.
reference reference = 180o ­ θ
reference = θ ­ 180o reference = 360o ­ θ
Find the reference angle for each given angle.
EX 1
210o
EX 2
300o
EX 3
­240 o
EX 4
1035o
­240o + 360o = 120o 1035o­ 2(360o) = 315o
coterminal angle
Quadrant III
210o ­ 180o = 30o
reference = 30o
Quadrant IV
360o ­ 300o = 60o
reference = 60o
Quadrant II
180o ­ 120o = 60o
reference = 60o
coterminal angle
Quadrant IV
360o ­ 315o = 45o
reference = 45o
Quadrant I
Quadrant II
reference = 180o ­ θ
reference θ
Reference Angle
θ
Reference Angle
120 o 60 o 30o 30 o 135 o 45 o 45o 45 o 150 o 30 o 60o 60 o Quadrant IV
Quadrant III
reference = θ ­ 180o reference = 360o ­ θ
θ
Reference Angle
θ
Reference Angle
210 o 30 o 300 o 60 o 225 o 45 o 315 o 45 o 240 o 60 o 330 o 30 o 5, then it has a reference angle of 45o.
If the degree ends in a 30o.
o
If the degree's middle number is EVEN, then it has a reference angle of 60 .
If the degree's middle number is ODD, then it has a reference angle of Finding the Trigonometric Values of Special Angles
Step 1: Determine what quadrant the angle is in.
Step 2: Determine whether or not the value will be positive or negative.
Step 3: Find the reference angle (30o, 45o, 60o).
Step 4: Determine the value for the given reference angle.
All Students Take Classes
EX 5
sin120o
EX 6
cos225o
EX 7
tan 330o
Finding the Trigonometric Values of Special Angles
Step 1: Determine what quadrant the angle is in.
Step 2: Determine whether or not the value will be positive or negative.
Step 3: Find the reference angle (30o, 45o, 60o).
Step 4: Determine the value for the given reference angle.
All Students Take Classes
EX 8
csc 60o
EX 9
sec 210o
EX 10
cot 135o
Finding Angle Measures Given Trigonometric Function Values
Step 1: Find the quadrants of the trigonometric function by its charge.
Step 2: Find the reference angle by the function value.
Step 3: Use the reference angle to find its angle measure, , in the interval of [0o, 360o]. EX 11
EX 12
EX 13
EX 14
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