If the line y = mx + c is a tangent to the circle x^2 +... – Geometry

Geometryhard · Past Paper

If the line y = mx + c is a tangent to the circle x^2 + y^2 = a^2, then the condition is:

Ac^2 = a^2(1 + m^2)

Bc^2 = a^2 / (1 + m^2)

Cc = am

Dc^2 = a^2(1 - m^2)

✓ Correct Answer: A — c^2 = a^2(1 + m^2)

The perpendicular distance from origin (0,0) to mx - y + c = 0 must equal radius 'a'. |c|/sqrt(m^2+1) = a => c^2 = a^2(1+m^2).

Share this question