Trig Fns - Identities
Interactive practice questions
By using the expansion of $\cos\left(A+B\right)$cos(A+B), verify $\cos2x=2\cos^2\left(x\right)-1$cos2x=2cos2(x)−1.
Easy
4min
By using the expansion of $\sin\left(A+B\right)$sin(A+B), verify that $\sin2x=2\sin x\cos x$sin2x=2sinxcosx.
Easy
1min
By simplifying the left hand side (LHS) of the identity, verify that $\sin\left(x+y\right)-\sin\left(x-y\right)=2\cos x\sin y$sin(x+y)−sin(x−y)=2cosxsiny.
Easy
2min
By simplifying the left hand side (LHS) of the identity, verify that $\cos\left(x+210^\circ\right)+\sin\left(x+120^\circ\right)=0$cos(x+210°)+sin(x+120°)=0.
Easy
6min
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