Find cos(-23π/4) exactly, and as a decimal to 3 places.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Find exactly, and as a decimal to 3 places.
Need a reminder? The key ideaShow
Take away whole turns of , find the acute angle that makes with the x-axis, and give the value the sign of the quadrant. Positive in quadrants I to IV: all; sin and cosec; tan and cot; cos and sec. Sin, cos, sec and cosec have period ; tan and cot have period .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Add whole turns. .
Step 2. The value. .
Answer: .
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