Finding Perpendicular Lines to y=0.25x and Tangent to f(x)=1/x

In summary, the conversation discusses finding two straight lines that are perpendicular to y=0.25x and tangent to the curve f(x) = 1/x. The solution involves equating y and f(x) and determining the points of intersection, then using the derivative of f(x) to find the slope of the tangent lines and equate it to the slope of the perpendicular lines. The resulting equations are y = -4x + 17/2 and y = -4x - 17/2. The conversation also clarifies the process and possibilities for x and y values.
  • #1
fghtffyrdmns
145
0

Homework Statement



Find two straight lines that are perpendicular to y=0.25x and tangent to the curve f(x) = 1/x.

Homework Equations



y=0.25x
f(x) = 1/x.

The Attempt at a Solution



What I did was equate y and f(x) and determined when they equal which is 2 and -2. The points are (2, 1/2) and (-2,-1/2).

Now, I took the derivative of f(x) and got -1/x^2. Would I use this to find the slope at the two points? Then I could make the equation.
 
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  • #2
If the lines are perpendicular to y=(1/4)*x then what should the slopes of the tangent lines be? The slopes of the tangent lines should also be f'(x), right?
 
  • #3
If the lines are perpendicular to y=0.25x, what is their slope?
 
  • #4
Dick said:
If the lines are perpendicular to y=(1/4)*x then what should the slopes of the tangent lines be? The slopes of the tangent lines should also be f'(x), right?

The slope would be -4, no?

I've made the two equations of y = -4x + 17/2 and y = -4x -17/2.
 
  • #5
The -4x is right, but your y-intercept is wrong. Now that you have the slope of the lines, what does the relationship have to be between that slope and f'(x) in order for the lines to be tangent to f(x)?
 
  • #6
fghtffyrdmns said:
The slope would be -4, no?

I've made the two equations of y = -4x + 17/2 and y = -4x -17/2.

Yes, the slope should be -4. But how did you get those two line equations?
 
  • #7
Dick said:
Yes, the slope should be -4. But how did you get those two line equations?

I equated y and f(x) to see when they intercept. I got 2 and -2. I put these two into f(x) to get the y cordinate so I can make the equation as I have the slope.
 
  • #8
fghtffyrdmns said:
I equated y and f(x) to see when they intercept. I got 2 and -2. I put these two into f(x) to get the y cordinate so I can make the equation as I have the slope.

I'm still not totally clear what you are doing. But if you know the slope is -4, then f'(x) should be -4, right? What are the possibilities for x?
 
  • #9
Dick said:
I'm still not totally clear what you are doing. But if you know the slope is -4, then f'(x) should be -4, right? What are the possibilities for x?

Ahhh, I equate the slope to -4. The possibilities of x are 1/2 and -1/2?
 
  • #10
Yes! If you know x=1/2 or -1/2, then you know y. So now you know x and y and the slope. Pretty easy, right?
 
  • #11
Dick said:
Yes! If you know x=1/2 or -1/2, then you know y. So now you know x and y and the slope. Pretty easy, right?

y = just 2 and -2.

Yes, sir. Dang my silly mistake :[. Thank you!
 

Related to Finding Perpendicular Lines to y=0.25x and Tangent to f(x)=1/x

1. How do you find the slope of a line perpendicular to y=0.25x?

To find the slope of a line perpendicular to y=0.25x, you need to take the negative reciprocal of the slope of y=0.25x. In this case, the slope of y=0.25x is 0.25, so the slope of the perpendicular line would be -4.

2. What is the equation of a line that is perpendicular to y=0.25x and passes through a given point?

The equation of a line that is perpendicular to y=0.25x and passes through a given point (x1, y1) can be found using the point-slope formula. The slope of the perpendicular line would be -4, so the equation would be y - y1 = -4(x - x1).

3. How do you prove that two lines are perpendicular?

To prove that two lines are perpendicular, you need to show that their slopes are negative reciprocals of each other. In this case, the slope of y=0.25x is 0.25, and the slope of the perpendicular line would be -4, which are negative reciprocals of each other.

4. How do you find the equation of a line that is tangent to f(x)=1/x?

To find the equation of a line that is tangent to f(x)=1/x, you need to find the derivative of f(x) and evaluate it at the point where the tangent line touches the curve. This will give you the slope of the tangent line, and you can use the point-slope formula to find the equation.

5. What is the relationship between perpendicular lines and tangent lines?

Perpendicular lines and tangent lines are both types of lines that intersect with other lines or curves. Perpendicular lines intersect at a 90-degree angle, while tangent lines intersect at a single point on a curve. In this case, the perpendicular line to y=0.25x will intersect the curve f(x)=1/x at a 90-degree angle, making it a tangent line.

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