The height of an isosceles triangle with equal sides x each and base y is given by

• A. \(\sqrt {{x^y} - {y^2}} \)
• B. \(\frac{{\sqrt {{x^2} - 4{y^2}} }}{2}\)
• C. \(\frac{{\sqrt {4{x^2} - {y^2}} }}{2}\)
• D. \(\frac{{\sqrt {{y^2} - 4{x^2}} }}{2}\)