• #### Other Forms of the Cosine Double-Angle Formula - Concept

How to derive two more cosine double-angle formulas.
• #### Other Forms of the Cosine Double-Angle Formula - Concept

How to derive two more cosine double-angle formulas.
• #### Other Forms of the Cosine Double-Angle Formula - Problem 1

How to use the cosine double-angle formulas to derive the power reduction formulas.
• #### Other Forms of the Cosine Double-Angle Formula - Problem 1

How to use the cosine double-angle formulas to derive the power reduction formulas.
• #### The Double-Angle Formulas - Concept

How to use the sine and cosine addition formulas to prove the double-angle formulas.
• #### The Double-Angle Formulas - Concept

How to use the sine and cosine addition formulas to prove the double-angle formulas.
• #### The Double-Angle Formulas - Problem 2

How to derive a triple-angle formula for cosine.
• #### The Double-Angle Formulas - Problem 2

How to derive a triple-angle formula for cosine.
• #### Other Forms of the Cosine Double-Angle Formula - Problem 2

How to use the power reduction formulas to reduce cos4 x.
• #### Other Forms of the Cosine Double-Angle Formula - Problem 2

How to use the power reduction formulas to reduce cos4 x.
• #### The Double-Angle Formulas - Problem 1

How to use the sine and cosine double-angle formulas to find sin(2a) and cos(2a) when sin(a) is known.