Difference between revisions of "Relationship between arctan and arccot"
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Let $y = \arctan \left( \dfrac{1}{z} \right)$. Then since arctan is the [[inverse function]] of [[tangent]], | Let $y = \arctan \left( \dfrac{1}{z} \right)$. Then since arctan is the [[inverse function]] of [[tangent]], | ||
$$\tan(y)=\dfrac{1}{z}.$$ | $$\tan(y)=\dfrac{1}{z}.$$ | ||
| − | + | By the definition of cotangent, we get | |
$$\cot(y)=z.$$ | $$\cot(y)=z.$$ | ||
Since $\mathrm{arccot}$ is the inverse function of $\cot$, take the $\mathrm{arccot}$ of each side to get | Since $\mathrm{arccot}$ is the inverse function of $\cot$, take the $\mathrm{arccot}$ of each side to get | ||
Latest revision as of 14:45, 25 September 2016
Theorem
The following formula holds: $$\mathrm{arctan}(z) = \mathrm{arccot}\left( \dfrac{1}{z} \right),$$ where $\mathrm{arctan}$ denotes the inverse tangent and $\mathrm{arccot}$ denotes the inverse cotangent.
Proof
Let $y = \arctan \left( \dfrac{1}{z} \right)$. Then since arctan is the inverse function of tangent, $$\tan(y)=\dfrac{1}{z}.$$ By the definition of cotangent, we get $$\cot(y)=z.$$ Since $\mathrm{arccot}$ is the inverse function of $\cot$, take the $\mathrm{arccot}$ of each side to get $$y = \mathrm{arccot}(z).$$ Therefore we have shown $$\arctan \left( \dfrac{1}{z} \right) = \mathrm{arccot}(z),$$ as was to be shown.
