show that the lengths of the tangents from the point to the circle are

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equation of a circle: (x + f)^2 + (y + g)^2 = 2 - c = (sqrt(2 - c))^2.

a line tangent to circle forms a right triangle, where the point of tangency as the right angle, one point at the center of a circle (-f,-g) and the other at a certain point (h,k.)

use distance formula . . . .