Answer:
see explanation
Step-by-step explanation:
Using the identity
tan x = [tex]\frac{sinx}{cosx}[/tex]
Consider the left side
[tex]\frac{1-tan^2x}{1+tan^2x}[/tex]
= [tex]\frac{1-\frac{sin^2x}{cos^2x} }{1+\frac{sin^2x}{cos^2x} }[/tex] ( multiply numerator and denominator by cos²x to clear fractions
= [tex]\frac{cos^2x-sin^2x}{cos^2x+sin^2x}[/tex] ← ( cos²x + sin²x = 1 ]
= cos²x - sin²x
= right side , thus proven
