Related Formula
y = mx - 2am - am³ (Equation of normal to y² = 4ax)$$y = mx - 2am - am^3 \quad \text{(Equation of normal to } y^2 = 4ax)$$
Core Logic
First, extract the centre C$C$ of the circle x² + y² - 4x - 16y + 64 = 0$x^2 + y^2 - 4x - 16y + 64 = 0$:
C ≡ (2, 8)$C \equiv (2, 8)$
For the parabola y² = 4x$y^2 = 4x$, comparing with y² = 4ax$y^2 = 4ax$, we get a = 1$a = 1$.
The shortest distance between a point and a curve is measured along the normal to the curve passing through that point. We need the normal to the parabola that passes through the circle's centre (2, 8)$(2, 8)$.
Step 1: Applying Normal Condition
Equation of normal in slope form (a=1$a=1$):
y = mx - 2m - m³$$y = mx - 2m - m^3$$
Since it passes through (2, 8)$(2, 8)$:
8 = m(2) - 2m - m³$$8 = m(2) - 2m - m^3$$
8 = -m³ ⇒ m³ = -8 ⇒ m = -2$$8 = -m^3 \Rightarrow m^3 = -8 \Rightarrow m = -2$$
Step 2: Finding Coordinate Point on Parabola
The foot of the normal on the parabola is given by the coordinate P(am², -2am)$P(am^2, -2am)$.
Substitute a=1, m=-2$a=1, m=-2$:
P ≡ (1(-2)², -2(1)(-2))$$P \equiv (1(-2)^2, -2(1)(-2))$$
P ≡ (4, 4)$P \equiv (4, 4)$
Step 3: Calculating Shortest Distance
The distance d$d$ is between the point P(4, 4)$P(4, 4)$ and the centre C(2, 8)$C(2, 8)$:
d = √((4-2)² + (4-8)²)$$d = \sqrt{(4-2)^2 + (4-8)^2}$$
d = √(2² + (-4)²) = √(4 + 16) = √(20)$$d = \sqrt{2^2 + (-4)^2} = \sqrt{4 + 16} = \sqrt{20}$$
Thus, d² = 20$d^2 = 20$.
Pattern Recognition
Shortest distance between a curve and a fixed point (like a circle's center) ALWAYS lies exactly along their common normal. Write the parameterized normal equation and force it through the coordinate to extract the slope root.
Chapter Mix
Class 11 Maths: Circles
Class 11 Maths: Parabola