Answer:
To prove :
cos36° + sin36° / cos36° - sin36° = tan81°
Step-by-step explanation:
STEP 1 :
First, we consider the Left Hand Side (LHS),
[tex]\frac{cos 36^{0} + sin 36^{0} }{cos 36^{0} - sin 36^{0}}[/tex]
STEP 2 :
Now, divide each term by cos36°, we get
⇒ [tex]\frac{\frac{cos 36^{0} }{cos 36^{0} } + \frac{sin 36^{0} }{cos 36^{0} } }{\frac{cos 36^{0} }{cos 36^{0} } - \frac{sin 36^{0} }{cos 36^{0} } }[/tex]
⇒ [tex]\frac{1 + \frac{sin 36^{0} }{cos 36^{0} } }{1 - \frac{sin 36^{0} }{cos 36^{0} }}[/tex]
STEP 3 :
By trigonometric identities, we know that [tex]\frac{sin \alpha }{cos \alpha } = tan \alpha[/tex] , so we write
⇒ [tex]\frac{1 + tan 36^{0} }{1 - tan 36^{0} }[/tex]
since we rewrite the above equation as
⇒ [tex]\frac{1 + tan 36^{0} }{1 - 1. tan 36^{0} }[/tex]
STEP 4 :
We know that tan 45° = 1, the above equation is written as
⇒ [tex]\frac{tan 45^{0} + tan 36^{0} }{1 - tan 45^{0} .tan 36^{0} }[/tex] -----> (1)
STEP 5 :
From the formula, [tex]tan ( \alpha +\beta ) = \frac{tan \alpha + tan \beta }{1 - tan\alpha .tan \beta }[/tex] -------> (2)
By comparing the equation (1) and (2), we write
α = 45° and β = 36°
STEP 6 :
Hence, tan (α + β) = tan (45° + 36°)
= tan 81°
= RHS
∴ LHS = RHS
Thus, cos36° + sin36° / cos36° - sin36° = tan81°
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