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- How To Find The Reference Angle In Radians and Degrees - Trigonometry
How To Find The Reference Angle In Radians and Degrees - Trigonometry
This trigonometry video tutorial provides a basic introduction into reference angles. It explains how to find the reference angle in radians and degrees.
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Video Transcript
now let's talk about reference angles
and how to find them
so let's say if we have an angle
of 120 degrees
what is the reference angle
so let's draw 120 degrees 120
is in quadrant two
so this is 120 relative to the positive
x-axis
the reference angle
is the angle between the x-axis
and the terminal side or the terminal
array
and it's always less than 90. it's
between 0 and 90.
so what is the angle here
to find that angle we know it's
if this angle is 180
and this is 120 it has to be the
difference between the two
so it's 180 minus
120
so this angle is 60 and that's the
reference angle
so let's try another example what is the
reference angle
for an angle that's 210 relative to
positive x-axis
so this is 210
and we know the negative x-axis is 180.
so the difference is 30.
so the reference angle is always between
a terminal ray and the x-axis
now there are some equations that you
can use to easily find the reference
angle
so anytime you have an angle in quadrant
one the reference angle
is equal to the angle in quadrant one
if you have an angle in quadrant two the
reference angle
is going to be 180 minus the angle in
quadrant two
if the angle is in quadrant three
the reference angle
is going to be the angle in quadrant
three minus 180
now if the angle is in quadrant four
then it's going to be 360 minus the
angle in quadrant four