Q35 of 63 Page 202

State whether the statements True or False. Justify

If the line lx + my = 1 is a tangent to the circle x2 + y2 = a2, then the point (l, m) lies on a circle.

lx + my = 1


my = 1 – lx



Slope of tangent = -l


x2 + y2 = a2


(x – 0) 2 + (y – 0) 2 = a2


Centre = (0, 0) Radius = a units


Slope of line perpendicular to tangent= {Product of slopes of perpendicular lines = -1}


Equation of line perpendicular to tangent i.e.., Radius of the circle



ly = x – 0


Distance of centre (0,0) from the line lx + my = 1 is equal to the radius ‘a’.


Perpendicular Distance (Between a point and line) = , whereas the point is and the line is expressed as ax + by + c = 0






Squaring both the sides,



Hence, the locus of (l,m)is, which is a circle.


TRUE


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