Is $ tan(arctan(frac{1}{x})) $ equal to infinity?












0














I am solving the equation below:
$$
S = pi (4 - (p . tan(arctan(frac{1}{p}))^2)
$$

My solution for solving $ tan(arctan(frac{1}{p})) $ is:
$$
tan(arctan(frac{1}{p})) =
tan(frac{pi}{2} - arctan(p)) =
frac{tan(frac{pi}{2}) - tan(arctan(p))}{ 1 + tan(frac{pi}{2})
.tan(arctan(p))} =
$$

$$
frac{∞ - p}{1 + ∞ . p} =
frac{∞}{∞}
$$

I know it is wrong! Please determine my mistake(s) and show me how to solve such equations. thanks!










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  • 4




    The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
    – Mark Viola
    Jan 4 at 18:28


















0














I am solving the equation below:
$$
S = pi (4 - (p . tan(arctan(frac{1}{p}))^2)
$$

My solution for solving $ tan(arctan(frac{1}{p})) $ is:
$$
tan(arctan(frac{1}{p})) =
tan(frac{pi}{2} - arctan(p)) =
frac{tan(frac{pi}{2}) - tan(arctan(p))}{ 1 + tan(frac{pi}{2})
.tan(arctan(p))} =
$$

$$
frac{∞ - p}{1 + ∞ . p} =
frac{∞}{∞}
$$

I know it is wrong! Please determine my mistake(s) and show me how to solve such equations. thanks!










share|cite|improve this question


















  • 4




    The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
    – Mark Viola
    Jan 4 at 18:28
















0












0








0







I am solving the equation below:
$$
S = pi (4 - (p . tan(arctan(frac{1}{p}))^2)
$$

My solution for solving $ tan(arctan(frac{1}{p})) $ is:
$$
tan(arctan(frac{1}{p})) =
tan(frac{pi}{2} - arctan(p)) =
frac{tan(frac{pi}{2}) - tan(arctan(p))}{ 1 + tan(frac{pi}{2})
.tan(arctan(p))} =
$$

$$
frac{∞ - p}{1 + ∞ . p} =
frac{∞}{∞}
$$

I know it is wrong! Please determine my mistake(s) and show me how to solve such equations. thanks!










share|cite|improve this question













I am solving the equation below:
$$
S = pi (4 - (p . tan(arctan(frac{1}{p}))^2)
$$

My solution for solving $ tan(arctan(frac{1}{p})) $ is:
$$
tan(arctan(frac{1}{p})) =
tan(frac{pi}{2} - arctan(p)) =
frac{tan(frac{pi}{2}) - tan(arctan(p))}{ 1 + tan(frac{pi}{2})
.tan(arctan(p))} =
$$

$$
frac{∞ - p}{1 + ∞ . p} =
frac{∞}{∞}
$$

I know it is wrong! Please determine my mistake(s) and show me how to solve such equations. thanks!







trigonometry inverse-function






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asked Jan 4 at 18:21









Amir ForsatiAmir Forsati

1086




1086








  • 4




    The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
    – Mark Viola
    Jan 4 at 18:28
















  • 4




    The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
    – Mark Viola
    Jan 4 at 18:28










4




4




The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
– Mark Viola
Jan 4 at 18:28






The range of the arctangent is $[-pi/2,pi/2]$. On the domain $(-pi/2,pi/2)$, the range of the tangent is $(-infty,infty)$. Hence, $tan(arctan(x))=x$ for all $xin mathbb{R}$. Is your expression $tan left( arctanleft(frac1pright)times arctanleft(frac1pright)right)?$ Or is your expression $tan left( arctanleft(frac1pright)right)times tan left( arctanleft(frac1pright)right)$
– Mark Viola
Jan 4 at 18:28












1 Answer
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I'm not a trig identity wizard but I can tell you that $tan(arctan(x))=x$ as the definition of arctan is the inverse of tan. So you don't need to do all those manipulations to solve for $tan(arctan(frac{1}{p}))$ as that is just $frac{1}{p}$. This is consistent with your answer as what you got is undefined and could be any value.






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  • Thanks for your answer, I got it. but why is my method wrong?
    – Amir Forsati
    Jan 4 at 18:48











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1 Answer
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active

oldest

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1 Answer
1






active

oldest

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active

oldest

votes






active

oldest

votes









1














I'm not a trig identity wizard but I can tell you that $tan(arctan(x))=x$ as the definition of arctan is the inverse of tan. So you don't need to do all those manipulations to solve for $tan(arctan(frac{1}{p}))$ as that is just $frac{1}{p}$. This is consistent with your answer as what you got is undefined and could be any value.






share|cite|improve this answer





















  • Thanks for your answer, I got it. but why is my method wrong?
    – Amir Forsati
    Jan 4 at 18:48
















1














I'm not a trig identity wizard but I can tell you that $tan(arctan(x))=x$ as the definition of arctan is the inverse of tan. So you don't need to do all those manipulations to solve for $tan(arctan(frac{1}{p}))$ as that is just $frac{1}{p}$. This is consistent with your answer as what you got is undefined and could be any value.






share|cite|improve this answer





















  • Thanks for your answer, I got it. but why is my method wrong?
    – Amir Forsati
    Jan 4 at 18:48














1












1








1






I'm not a trig identity wizard but I can tell you that $tan(arctan(x))=x$ as the definition of arctan is the inverse of tan. So you don't need to do all those manipulations to solve for $tan(arctan(frac{1}{p}))$ as that is just $frac{1}{p}$. This is consistent with your answer as what you got is undefined and could be any value.






share|cite|improve this answer












I'm not a trig identity wizard but I can tell you that $tan(arctan(x))=x$ as the definition of arctan is the inverse of tan. So you don't need to do all those manipulations to solve for $tan(arctan(frac{1}{p}))$ as that is just $frac{1}{p}$. This is consistent with your answer as what you got is undefined and could be any value.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Jan 4 at 18:29









Keefer RowanKeefer Rowan

1386




1386












  • Thanks for your answer, I got it. but why is my method wrong?
    – Amir Forsati
    Jan 4 at 18:48


















  • Thanks for your answer, I got it. but why is my method wrong?
    – Amir Forsati
    Jan 4 at 18:48
















Thanks for your answer, I got it. but why is my method wrong?
– Amir Forsati
Jan 4 at 18:48




Thanks for your answer, I got it. but why is my method wrong?
– Amir Forsati
Jan 4 at 18:48


















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