Equation of the diameter of the circle x2+y2−2x+4y=0 which passes through the origin is
2x+y=0
Let the diameter of the circle be y = mx Since the diameter of the circle passes through its centre, (1, -2) satisfies the equation of the diameter.
∴m=−2
Substituting the value of m in the equation of diameter.
y=−2x
⇒2x+y=0
Hence, the required equation of the diameter is 2x+y=0