Trigonometry (11th Edition) Clone

Published by Pearson
ISBN 10: 978-0-13-421743-7
ISBN 13: 978-0-13421-743-7

Chapter 5 - Trigonometric Identities - Section 5.5 Double-Angle Identities - 5.5 Exercises - Page 237: 29

Answer

$$\tan x+\cot x=2\csc2x$$ The equation is an identity, as the left side is equal to the right one.

Work Step by Step

$$\tan x+\cot x=2\csc2x$$ The right side would be taken into consideration first. $$X=2\csc2x$$ We know that $\csc\theta=\frac{1}{\sin\theta}$, so $\csc2x=\frac{1}{\sin2x}$. $$X=\frac{2}{\sin2x}$$ Now $\sin 2x=2\sin x\cos x$, as stated in Double-Angle Identities. $$X=\frac{2}{2\sin x\cos x}$$ $$X=\frac{1}{\sin x\cos x}$$ We can rewrite $1$ as $\sin^2x+\cos^2x$, as they also equal $1$. $$X=\frac{\sin^2x+\cos^2x}{\sin x\cos x}$$ $$X=\frac{\sin^2x}{\sin x\cos x}+\frac{\cos^2x}{\sin x\cos x}$$ $$X=\frac{\sin x}{\cos x}+\frac{\cos x}{\sin x}$$ Applying Quotient Identities: $\frac{\sin x}{\cos x}=\tan x$ and $\frac{\cos x}{\sin x}=\cot x$. $$X=\tan x+\cot x$$ Thus, $$\tan x+\cot x=2\csc2x$$ The equation is an identity, as the left side is equal to the right one.
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