Hello, qbkr21!
Be careful! . . .
Given: . and is in
Find: .
Identity: .
So we have: . . . . which you already knew
Since is in
. . Hence, is in Quadrant 2, where sine is positive.
Therefore: . +
For example if I am given:
and is in
in quadrant III
I worked it out in by using the half angle formula and got
I usually use the old inverse trick on the calculator and check to see if the decimal I get matches the answer I got. But on several half angle problems I am getting an undefined message on my calc. What is the deal and how can I go about checking these...
Like what PerfectHacker did on this post http://www.mathhelpforum.com/math-he...i-89-calc.html
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Also one other question.... When I am using the double angle and half angle formulas, when I get what the single trig value is equal to such as and I am going to stick the value in a problem do I want to insert the negative or positive sign along with it depending on which quadrant I am talking about? For example in the problem above we are in the 3rd quadrant so both & both are negative. Would I want to insert them into the formulas as negative? But suppose we are in quadrant 1 where both & are positive. Would I want to put both values into the double or half-angle formulas as a postive?
I could use some real help with both questions if you could...
Thanks as always for the help!