How Can You Find a Function Tangent to Specific Lines at Given Points?

Click For Summary
SUMMARY

The discussion focuses on finding a function of the form f(x) = a + bcos(cx) that is tangent to the line y = 1 at the point (0, 1) and tangent to the line y = x + 3/2 - π/4 at the point (π/4, 3/2). The problem requires the application of differentiation and implicit differentiation to derive two equations from the tangency conditions, resulting in four equations for three unknowns (a, b, c). This transforms the problem from a calculus exercise into an algebraic challenge, necessitating the formulation of equations based on the values of f(x) and its derivative at specified points.

PREREQUISITES
  • Understanding of calculus concepts, specifically differentiation and implicit differentiation.
  • Familiarity with trigonometric functions, particularly cosine functions.
  • Ability to solve systems of equations involving multiple variables.
  • Knowledge of tangent lines and their properties in calculus.
NEXT STEPS
  • Learn how to derive equations from tangency conditions in calculus.
  • Study the method of solving systems of equations with more equations than unknowns.
  • Explore the properties of trigonometric functions and their derivatives.
  • Investigate the application of implicit differentiation in solving complex problems.
USEFUL FOR

Students studying calculus, particularly those tackling problems involving tangents and trigonometric functions, as well as educators looking for examples of algebraic transformations in calculus contexts.

MC Escher
Messages
13
Reaction score
0

Homework Statement


Find a function of the form f(x)=a+bcos(cx) that is tangent to the line y=1 at the point (0,1), and tangent to the line y=x+3/2-pi/4 at the point (pi/4, 3/2).


Homework Equations


I know that the problem involves differentiation and implicit differentiation. I don't really think there are many "equations" that I could give that would help, besides may the limit definition.


The Attempt at a Solution


I haven't made it very far, but I am quite sure you need to somehow separate a, b, and c and than eliminate c altogether. I also have been trying odd and even values for c...
all help is appreciated, thanks...
 
Physics news on Phys.org
"Tangent at a point (a,b)" requires two degrees of freedom. The two curves have to both go through (a,b), and the two curves have to have the same deriviative.

This means that you will get two equations for each "tangent at a point" restriction. You've got two such restrictions, so you should be able to get 2x2 = 4 equations from the tangent restrictions.

There are only 3 unknown constants to solve for, a,b,c, so the problem might be over determined. In any case, this turns the problem from a calculus problem, which you are learning (i.e. find the slope of a curve), to an algebra problem (i.e. solve four equations in three unknowns) which you learned the technique in a previous class.

So go for it!
 
The tangency conditions give you requirements on the value of f(x) and f'(x) at various points. Write these equations down and if you are having problems people will try to help you. I'll get you started, f(0)=1.
 
thanks for the help so far...
 
y= 3/2 - (1/2)cos(2x)
 
holarjc said:
y= 3/2 - (1/2)cos(2x)

You are i) violating the forum rules by supplying an solution instead of hints on how to solve it (even if it is right, which I haven't checked) and ii) this thread is two years old. What's your point?
 

Similar threads

Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
1
Views
1K
Replies
3
Views
2K
Replies
3
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
13
Views
4K