Find the equation of tangent for ellipse $\large\frac{x^2}{a^2}+\frac{y^2}{b^2}$$=1$?

Question

$\begin{array}{1 1}(a)\;\large\frac{xx_1}{a^2}+\frac{yy_1}{b^2}\normalsize=1\\(b)\;\large\frac{xx_1}{a^2}-\frac{yy_1}{b^2}\normalsize=1\\(c)\;\large\frac{xx_1}{a^3}+\frac{yy_1}{b^3}\normalsize=1\\(d)\;\text{None of these}\end{array}$