Equation of plane tangent to sphere centered at the origin

Question

What is the equation of the plane tangent to a sphere centered at the origin? The sphere has radius d, and the point of tangency is at (x1, y1, z1). Is there an equation for this plane, while still preserving all four variables?

Thank you in advance.

Answer 1

$$({\bf p}-(x_1, y_1, z_1))^t (x_1, y_1, z_1) = 0$$

or

$${\bf p}^t (x_1, y_1, z_1) = 1$$