the line Ax+By+C=0 will touch the circle x^2+y^2=lamda when????

answer is given as C^=lamda(A^+B^)

Here AX + B Y + C is equal to zero touches the circle x squared plus y squared is equal to Lambda that means that line is tangent to the circle so the distance between the centre of the circle to line is equal to the radius of the circle therefore Mod modulus of c by under root of a square + b square is equal to root Lambda now squaring on both sides you'll get c-square by a square + b square is equal to Lambda so she square is equal to London into a square + b square the radius of the circle is equal to root Lambda