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If xyztan-1x+tan-1y+tan-1z=π2, then show that xy + yz + zx = 1 - Mathematics and Statistics

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Question

If `tan^-1 "x" + tan^-1 "y" + tan^-1 "z" = pi/2,` then show that xy + yz + zx = 1

Sum
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Solution

`tan^-1 "x" + tan^-1 "y" + tan^-1 "z" = pi/2`

∴ `tan^-1 (("x + y")/(1 - "xy")) + tan^-1 "z" = pi/2`

∴ `tan^-1 [(("x + y")/(1 - "xy") + "z")/(1 - (("x + y")/(1 - "xy"))"z")] = pi/2`

∴ `tan^-1 [("x + y + z - xyz")/(1 - xy - xz - yz)] = pi/2`

∴ `("x + y + z - xyz")/(1 - "xy" - "yz" - "zx") = tan  pi/2`, which does not exist

∴ 1 - xy - yz - zx = 0

∴ xy + yz + zx = 1

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Trigonometric Equations and Their Solutions
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Chapter 3: Trigonometric Functions - Miscellaneous exercise 3 [Page 111]

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Balbharati Mathematics and Statistics 1 (Arts and Science) [English] Standard 12 Maharashtra State Board
Chapter 3 Trigonometric Functions
Miscellaneous exercise 3 | Q 38 | Page 111

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