Equation of the tangent to the curve x^{2}+y^{2}=a^{2} at \left(x_{1}, y_{1}\right) is (a) x x_{1}-y y_{1}=0 (b) x x_{1}+y y_{1}=0 (c) x x_{1}-y y_{1}=a^{2} (d) x x_{1}+y y_{1}=a^{2}
Equation of the tangent to the curve x^{2}+y^{2}=a^{2} at \left(x_{1}, y_{1}\right) is (a) x x_{1}-y y_{1}=0 (b) x x_{1}+y y_{1}=0 (c) x x_{1}-y y_{1}=a^{2} (d) x x_{1}+y y_{1}=a^{2}

SOL:
Correct option is D. x x_{1}+y y_{1}=a^{2}