If α and β are positive angles such that \(α + β = \dfrac{\pi}{4}\), then what is (1 + tan α) (1 + tan β) equal to?  

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Answer (Detailed Solution Below)

Option 3 : 2
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Detailed Solution

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Concept:

\(\rm \tan (α + β) = \dfrac {tan \alpha + tan \beta }{1 -tan \alpha \;tan \beta }\)

 

Calculations:

Given, α and β are positive angles such that \(α + β = \dfrac{\pi}{4}\)

\(\rm \tan (α + β) = \tan (\dfrac{\pi}{4})\)

\(\rm \dfrac {tan \alpha + tan \beta }{1 -tan \alpha \;tan \beta } = 1\)

\(\rm {tan \alpha + tan \beta }= 1 -tan \alpha \;tan \beta \)

\(\rm {tan \alpha +tan \alpha \;tan \beta + tan \beta } - 1 = 0 \)

\(\rm {tan \alpha +tan \alpha \;tan \beta + tan \beta } +1-2= 0 \)

\(\rm {tan \alpha +tan \alpha \;tan \beta + tan \beta } +1=2\)

\(\rm tan \alpha (1 +tan \beta ) + (1+tan \beta)=2\)

\(\rm (1+ tan \alpha )(1 +tan \beta )=2\)

Hence, If α and β are positive angles such that \(α + β = \dfrac{\pi}{4}\), then  (1 + tan α) (1 + tan β) equal to 2.  

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