1.

Show that the line (x – 2) cosθ + (y – 2) sinθ = 1 touches a circle for all values of θ. Find the circle. 

Answer»

Since the line (x – 2) cosθ + (y – 2) sinθ = 1 .......(1)

touches a circle so it is a tangent equation to a circle.

Equation of tangent to a circle at (x1 ,y1 ) is (x – h)x1 +(y – k)y1

= a2 to a circle (x – y)+ (y – k)=  a2 comparing (1) and (2) we get

x – h = x – 2 y – k = y – 2 and a2 = 1

x1 = 1cosθ  y1 = 1sinθ

∴ Required equation of circle is

(x – 2)2 + (y – 2)2 = 1

x2 + y– 4x – 4y + 7 = 0



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