Find line tangent to curve which is parallel to other line

Click For Summary

Homework Help Overview

The problem involves finding the line tangent to the curve defined by the function f(x) = 0.5x² + 3x - 1, which is parallel to the line g(x) = x/2 + 0.5. The discussion centers around the relationship between the slopes of the tangent line and the given line.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the necessity for the slopes of the tangent line and the given line to be equal. There is an exploration of how to find the point on the curve where the slope matches that of the line g(x).

Discussion Status

The discussion has progressed with participants identifying the slope of the tangent line and attempting to find the corresponding x-value where the derivative equals that slope. Some participants have noted arithmetic mistakes and are working towards correcting them.

Contextual Notes

There are indications of confusion regarding arithmetic calculations, and the need to adhere to the problem's requirements regarding derivatives and tangent lines is emphasized.

bubblescript
Messages
14
Reaction score
2

Homework Statement


Find the line tangent to the curve f(x)=0.5x2+3x-1 which is parallel to the line g(x)=x/2+0.5

Homework Equations


f'(x)=x+3

The Attempt at a Solution


I know it involves taking the derivative of f(x) and using it somehow, but I don't know where to go from there.
 
Physics news on Phys.org
bubblescript said:

Homework Statement


Find the line tangent to the curve f(x)=0.5x2+3x-1 which is parallel to the line g(x)=x/2+0.5

Homework Equations


f'(x)=x+3

The Attempt at a Solution


I know it involves taking the derivative of f(x) and using it somehow, but I don't know where to go from there.

You want to find the tangent line to the curve ##f(x)##, parallel to the line ##g(x)##. If the tangent line has to be parallel with ##g(x)##, what do you know about the slope of this line?
 
Both lines will need to have the same slope, 1/2.
 
bubblescript said:
Both lines will need to have the same slope, 1/2.

Correct. Now, the derivative gives the slope of the tangent line in each point. Where is the slope ##1/2##?
Can you find the equation of the tangent line then?
 
The slope is 1/2 when f'(x)=1/2:
1/2=x+3
x=-5/2
 
bubblescript said:
The slope is 1/2 when f'(x)=1/2:
1/2=x+3
x=5/2

Minor mistake in your arithmetic.

You have a slope and a point (if you fix the mistake). There is a unique line that fits those 2 conditions. Can you find the equation?
 
Yes caught the mistake.

So using -5/2 on f(x) gets f(-5/2)=-43/8, which means a point on the line is (-5/2, -43/8).
If the line is of the form y=1/2*x+b, we substitute the point for x and y:
-43/8=1/2*-5/2+b
b=-33/8
The line is: y=1/2*x-33/8
 
bubblescript said:
Yes caught the mistake.

So using -5/2 on f(x) gets f(-5/2)=-43/8, which means a point on the line is (-5/2, -43/8).
If the line is of the form y=1/2*x+b, we substitute the point for x and y:
-43/8=1/2*-5/2+b
b=-33/8
The line is: y=1/2*x-33/8

That's correct! Well done!
 
Thread moved. @bubblescript, please post problems that involve derivatives in the Calculus & Beyond section.
 
  • Like
Likes   Reactions: bubblescript

Similar threads

  • · Replies 8 ·
Replies
8
Views
2K
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K