If cos = x^2 - y^2x^2 + y^2 then the value of cot is equal to [ if 0^ 90^ ]

Answer: Option D

$$\text{cos}\theta =\frac{x^2-y^2}{x^2+y^2}$$

AC² = (x² + y²)² - (x² - y²)²
        = x⁴ + y⁴ + 2x²y² - x⁴ - y⁴ + 2x²y²
        = 4x²y²
⇒ AC = 2xy
⇒ cotθ = $$\frac{x^2-y^2}{2xy}$$