Find the equation of the circle passing through the point (2, 1) and touching the line x + 2y - 1 = 0 at the point (3, -1)
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Solution
Equation of circle is (x−3)2+(y+1)2+λ(x+2y−1)=0 Since it passes through the point (2,1),1+4+λ (2 + 2 - 1) = 0 ⇒λ=−53 ∴circleis(x−3)2+(y+1)2−53(x+2y−1)=0 ⇒3x2+3y2−23x−4y+35=0