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secondary 4 | A Maths
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Help to clear which quadrant need to choose
Date Posted: 3 years ago
Views: 160
I haven’t looked deep into this, but that angle is going to be either in the second or fourth.
Subtracting 90 degrees will make the new angle in either the first or third quadrant, both of which conflict each other.
There could well be two solutions.
But normally, we take this to be a fourth quadrant angle.
Because the principal angle for x lies between -90 and 90.
Subtracting 90 degrees will make the new angle in either the first or third quadrant, both of which conflict each other.
There could well be two solutions.
But normally, we take this to be a fourth quadrant angle.
Because the principal angle for x lies between -90 and 90.
So for your answer, use a fourth quadrant value in the spirit of the “principal values” for the inverses of sine, cosine and tangent.
Let tan A = -3/4 where A is a fourth quadrant angle in the range -pi/2 < A < 0.
After doing the “quadrant’s triangle”,
sin A = -3/5 and cos A = 4/5
sin (A - pi/2)
= sin A cos pi/2 - cos A sin pi/2
= (-3/5) (0) - (4/5) (1)
= -4/5
After doing the “quadrant’s triangle”,
sin A = -3/5 and cos A = 4/5
sin (A - pi/2)
= sin A cos pi/2 - cos A sin pi/2
= (-3/5) (0) - (4/5) (1)
= -4/5
Thank you.
See 2 Answers
Don't be too concern about which quadrant should take. Question should specify the range of values for the angle. Normally it is not by default taking the principle range unless question say so
Thank you
done
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