If the chord of contact of the tangents drawn from the point `(h , k)`
to the circle `x^2+y^2=a^2`
subtends a right angle at the center, then prove that `h^2+k^2=2a^2dot`
A. `h^(2)+k^(2)=a^(2)`
B. `2(h^(2)+k^(2))=a^(2)`
C. `h^(2)-k^(2)=a^(2)`
D. `h^(2)+k^(2)=2a^(2)`
