The Double-Angle Formulas - Concept

Concept Concept (1)

The double angles sin(2theta) and cos(2theta) can be rewritten as sin(theta+theta) and cos(theta+theta). Applying the cosine and sine addition formulas, we find that sin(2theta)=2sin(theta)cos(theta). Also, cos(2theta)=cos2(theta) - sin2(theta), see other forms for the two derivations. These results reappear in integral calculus, when remembering them can be the difference between a right and wrong answer.

Sample Sample Problems (2)

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The Double-Angle Formulas - Problem 1
Problem 1
How to use the sine and cosine double-angle formulas to find sin(2a) and cos(2a) when sin(a) is known.
The Double-Angle Formulas - Problem 2
Problem 2
How to derive a triple-angle formula for cosine.
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