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Prove 
(cot 54^(@))/(tan 36^(@))+(tan 20^(@))/(cot 70^(@))-2=0.

Prove cot54tan36+tan20cot702=0 \frac{\cot 54^{\circ}}{\tan 36^{\circ}}+\frac{\tan 20^{\circ}}{\cot 70^{\circ}}-2=0 .

Full solution

Q. Prove cot54tan36+tan20cot702=0 \frac{\cot 54^{\circ}}{\tan 36^{\circ}}+\frac{\tan 20^{\circ}}{\cot 70^{\circ}}-2=0 .
  1. Use Trigonometric Identities: We will use the fact that cot(θ)=1tan(θ)\cot(\theta) = \frac{1}{\tan(\theta)} and that tan(θ)=1cot(θ)\tan(\theta) = \frac{1}{\cot(\theta)}. We will also use the complementary angle identity, which states that tan(90°θ)=cot(θ)\tan(90° - \theta) = \cot(\theta) and cot(90°θ)=tan(θ)\cot(90° - \theta) = \tan(\theta).
  2. Simplify (cot54°)/(tan36°)(\cot 54°)/(\tan 36°): First, let's simplify (cot54°)/(tan36°)(\cot 54°)/(\tan 36°). Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta), we can rewrite cot54°\cot 54° as 1/tan54°1/\tan 54°. Therefore, (cot54°)/(tan36°)(\cot 54°)/(\tan 36°) becomes (1/tan54°)/(tan36°)(1/\tan 54°)/(\tan 36°).
  3. Simplify (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ): Simplifying the expression further, we get (1/tan54)/(tan36)=1/(tan54tan36)(1/\tan 54^\circ)/(\tan 36^\circ) = 1/(\tan 54^\circ \cdot \tan 36^\circ). Since tan(90θ)=cot(θ)\tan(90^\circ - \theta) = \cot(\theta), we can rewrite tan54\tan 54^\circ as cot(36)\cot(36^\circ). So, the expression becomes 1/(cot(36)tan36)1/(\cot(36^\circ) \cdot \tan 36^\circ).
  4. Substitute Simplified Expressions: Since cot(θ)tan(θ)=1\cot(\theta) \cdot \tan(\theta) = 1, the expression 1/(cot(36°)tan36°)1/(\cot(36°) \cdot \tan 36°) simplifies to 1/11/1, which is just 11. So, (cot54°)/(tan36°)(\cot 54°)/(\tan 36°) simplifies to 11.
  5. Calculate Final Result: Now, let's simplify (tan20°)/(cot70°)(\tan 20°)/(\cot 70°). Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta), we can rewrite cot70°\cot 70° as 1/tan70°1/\tan 70°. Therefore, (tan20°)/(cot70°)(\tan 20°)/(\cot 70°) becomes (tan20°)/(1/tan70°)(\tan 20°)/(1/\tan 70°).
  6. Calculate Final Result: Now, let's simplify tan20°cot70°\frac{\tan 20°}{\cot 70°}. Since cot(θ)=1tan(θ)\cot(\theta) = \frac{1}{\tan(\theta)}, we can rewrite cot70°\cot 70° as 1tan70°\frac{1}{\tan 70°}. Therefore, tan20°cot70°\frac{\tan 20°}{\cot 70°} becomes tan20°1tan70°\frac{\tan 20°}{\frac{1}{\tan 70°}}. Simplifying the expression further, we get tan20°1tan70°=tan20°tan70°\frac{\tan 20°}{\frac{1}{\tan 70°}} = \tan 20° \cdot \tan 70°. Since tan(90°θ)=cot(θ)\tan(90° - \theta) = \cot(\theta), we can rewrite tan70°\tan 70° as cot(20°)\cot(20°). So, the expression becomes cot(θ)=1tan(θ)\cot(\theta) = \frac{1}{\tan(\theta)}00.
  7. Calculate Final Result: Now, let's simplify (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ). Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta), we can rewrite cot70\cot 70^\circ as 1/tan701/\tan 70^\circ. Therefore, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) becomes (tan20)/(1/tan70)(\tan 20^\circ)/(1/\tan 70^\circ). Simplifying the expression further, we get (tan20)/(1/tan70)=tan20tan70(\tan 20^\circ)/(1/\tan 70^\circ) = \tan 20^\circ \cdot \tan 70^\circ. Since tan(90θ)=cot(θ)\tan(90^\circ - \theta) = \cot(\theta), we can rewrite tan70\tan 70^\circ as cot(20)\cot(20^\circ). So, the expression becomes cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00. Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)11, the expression cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00 simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33. So, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33.
  8. Calculate Final Result: Now, let's simplify (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ). Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta), we can rewrite cot70\cot 70^\circ as 1/tan701/\tan 70^\circ. Therefore, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) becomes (tan20)/(1/tan70)(\tan 20^\circ)/(1/\tan 70^\circ). Simplifying the expression further, we get (tan20)/(1/tan70)=tan20tan70(\tan 20^\circ)/(1/\tan 70^\circ) = \tan 20^\circ \cdot \tan 70^\circ. Since tan(90θ)=cot(θ)\tan(90^\circ - \theta) = \cot(\theta), we can rewrite tan70\tan 70^\circ as cot(20)\cot(20^\circ). So, the expression becomes cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00. Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)11, the expression cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00 simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33. So, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33. Now we have the simplified expressions: cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)66 and cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)77. Substituting these into the original equation, we get cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)88.
  9. Calculate Final Result: Now, let's simplify (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ). Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta), we can rewrite cot70\cot 70^\circ as 1/tan701/\tan 70^\circ. Therefore, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) becomes (tan20)/(1/tan70)(\tan 20^\circ)/(1/\tan 70^\circ). Simplifying the expression further, we get (tan20)/(1/tan70)=tan20tan70(\tan 20^\circ)/(1/\tan 70^\circ) = \tan 20^\circ \cdot \tan 70^\circ. Since tan(90θ)=cot(θ)\tan(90^\circ - \theta) = \cot(\theta), we can rewrite tan70\tan 70^\circ as cot(20)\cot(20^\circ). So, the expression becomes cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00. Since cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)11, the expression cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)00 simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33. So, (tan20)/(cot70)(\tan 20^\circ)/(\cot 70^\circ) simplifies to cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)33. Now we have the simplified expressions: cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)66 and cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)77. Substituting these into the original equation, we get cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)88. Adding the numbers together, we have cot(θ)=1/tan(θ)\cot(\theta) = 1/\tan(\theta)99. This proves that the original expression cot70\cot 70^\circ00 equals cot70\cot 70^\circ11.

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