Animated Solution for Mathematics - Conic Sections: The shortest distance between the curves y2=8x and x2+y2+12y+35=0 is :
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Visualized Solution
Visualizing the Curves
Given curves:
Parabola: y2=8x
Circle: x2+y2+12y+35=0
Analyzing the Circle
Standardizing the circle equation:
x2+(y2+12y+36)−36+35=0
x2+(y+6)2=1
Center C(0,−6), Radius r=1
The Shortest Distance Principle
Principle: Shortest distance lies along the common normal.
For a circle, the normal always passes through the center C(0,−6).
We need a normal to the parabola passing through (0,−6).
Equation of the Normal
For y2=8x, 4a=8⟹a=2.
Equation of normal in slope form (m):
y=mx−2am−am3
Substituting a=2:
y=mx−4m−2m3
Solving for Slope m
Normal passes through C(0,−6):
−6=m(0)−4m−2m3
2m3+4m−6=0
m3+2m−3=0
By inspection, m=1 is a root.
Finding Point P on Parabola
Point P on parabola for normal with slope m:
P(am2,−2am)
Substitute a=2,m=1:
P(2(1)2,−2(2)(1))=P(2,−4)
Calculating Distance PC
Distance between P(2,−4) and C(0,−6):
PC=(2−0)2+(−4−(−6))2
PC=22+22=8=22
Final Shortest Distance
Shortest distance d=PC−r
Substitute PC=22 and r=1:
d=22−1
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The Sigma Insight: Equation of Tangent and Normal
Solution Diagram
Analyzing the Setup
To find the shortest distance between the parabola y2=8x and the circle x2+y2+12y+35=0, we must first identify the geometric properties of both curves.
The parabola y2=8x is in the standard form y2=4ax, where 4a=8, implying a=2.
For the circle, we complete the square for the equation x2+y2+12y+35=0:
x2+(y2+12y+36)−36+35=0
x2+(y+6)2=1
Thus, the circle is centered at C(0,−6) with a radius r=1.
The Principle of the Normal
The shortest distance between two non-intersecting curves lies along their common normal. For a circle, any normal line must pass through its center C(0,−6).
Therefore, we must find a normal to the parabola y2=8x that passes through the point C(0,−6).
The Algebraic Battle
The equation of a normal to the parabola y2=4ax with slope m is given by:
y=mx−2am−am3
Substituting a=2 into this equation, we obtain:
y=mx−4m−2m3
Since this normal passes through C(0,−6), we substitute x=0 and y=−6:
−6=m(0)−4m−2m3
2m3+4m−6=0
m3+2m−3=0
By inspection, we find that m=1 is a root of this cubic equation.
Final Calculation
With the slope m=1, we determine the point of contact P on the parabola using the coordinates (am2,−2am):
P=(2(1)2,−2(2)(1))=(2,−4)
Next, we calculate the distance PC between the center C(0,−6) and the point P(2,−4):
PC=(2−0)2+(−4−(−6))2
PC=22+22=8=22
The shortest distance d between the parabola and the circle is the distance from the center to the parabola minus the radius of the circle:
d=PC−r
d=22−1
The minimum distance between the two curves is 22−1.