Tangent line and normal on a parabola

In summary, a tangent line on a parabola is a straight line that touches the curve at only one point, known as the point of tangency. The slope of the tangent line is equal to the slope of the parabola at that point. The equation of a tangent line can be written as y = mx + b, where m is the slope and b is the y-intercept. A normal line on a parabola is perpendicular to the tangent line at the point of tangency, forming a right angle. The equation of a normal line can be found by taking the negative reciprocal of the slope of the tangent line and using the point of tangency to determine the y-intercept.
  • #1
sooyong94
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2

Homework Statement


If the normal at P(ap^2 ,2ap) to the parabola y^2 = 4ax meets the curve again at Q(aq^2, 2aq), show that p^2 +pq+2=0

Homework Equations


Point-slope form

The Attempt at a Solution


Capture.jpg

I tried putting y=2aq and x=aq^2 but I can seem to simplify the whole thing other than dividing both sides by a
 
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  • #2
sooyong94 said:

Homework Statement


If the normal at P(ap^2 ,2ap) to the parabola y^2 = 4ax meets the curve again at Q(aq^2, 2aq), show that p^2 +pq+2=0

Homework Equations


Point-slope form

The Attempt at a Solution


Capture.jpg

I tried putting y=2aq and x=aq^2 but I can seem to simplify the whole thing other than dividing both sides by a
The expression is also dividable by q-p.
 
  • #3
Strangely enough I got this:
Capture.png
 
  • #4
sooyong94 said:
Strangely enough I got this:
Capture.png
There should be minus in front of the last term in the first equation. You made a mistake when copying.
 
  • #5
Thanks - worked that out quickly.
 
  • #6
Now I'm stuck on the second part:

Show that the equation of the locus of the point of intersection of the tangents at P and Q to the parabola is y^2(x+2a)+4a^3 =0. What does this mean? Does this mean that the tangents at P and Q meet at a point?

I managed to find the points of intersection of the two tangents (apq, a(p+q)), but I can't seem to continue at this point.
 
  • #7
sooyong94 said:
Show that the equation of the locus of the point of intersection of the tangents at P and Q to the parabola is y^2(x+2a)+4a^3 =0. What does this mean? Does this mean that the tangents at P and Q meet at a point?

I managed to find the points of intersection of the two tangents (apq, a(p+q)), but I can't seem to continue at this point.
You have to work with x and y. What are p and q now?
 
  • #8
x=apq
y=a(p+q)
 
  • #9
sooyong94 said:
x=apq
y=a(p+q)
Have you copied the question correctly? These x and y values do not fulfill the equation given y^2(x+2a)+4a^3 =0.
 
  • #10
I'm sorry - but I can't catch it.
 
  • #11
sooyong94 said:
I'm sorry - but I can't catch it.
I mean the problem might be wrong. The coordinates of the point of intersection do not fit to the given locus.
 

1. What is a tangent line on a parabola?

A tangent line on a parabola is a straight line that touches the curve of the parabola at only one point. This point of contact is called the point of tangency.

2. How is the slope of the tangent line related to the slope of the parabola at the point of tangency?

The slope of the tangent line is equal to the slope of the parabola at the point of tangency. This is because the tangent line and the parabola share the same direction at that point.

3. What is the equation of a tangent line on a parabola?

The equation of a tangent line on a parabola can be written in the form y = mx + b, where m is the slope of the tangent line and b is the y-intercept. To find the slope, you can use the derivative of the parabola's equation.

4. What is a normal line on a parabola?

A normal line on a parabola is a straight line that is perpendicular to the tangent line at the point of tangency. It intersects the parabola at the point of tangency and forms a right angle with the tangent line.

5. How can the equation of a normal line on a parabola be determined?

The slope of the normal line can be found by taking the negative reciprocal of the slope of the tangent line. Then, the equation can be written in the form y = mx + b, where m is the slope of the normal line and b is the y-intercept, which can be found by plugging in the point of tangency into the equation.

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