Lesson Writing a function rule for a function based on its wording description

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Writing a function rule for a function based on its wording description


Problem 1

The functions  f(x)  and  g(x)  are sine functions,  where   f(0) = g(0) = 0.
The amplitude of  f(x)  is twice the amplitude of  g(x).
The period of  f(x)  is one-half the period of  g(x).
If  g(x)  has a period of  2%2Api  and  f%28pi%2F4%29 = 4,  write the function rule for  g(x).

Solution

According to the problem, functions g(x) is sinusoidal, has the value of 0 at x= 0 
and has a period  2pi. Hence, g(x) has the form

    g(x) = b%2Asin%28x%29,  where real number "b" is the amplitude of g(x).


Function f(x) is sinusoidal, has the value of 0 at x= 0 and has a period, which is 
one-half of that of g(x), i.e. pi. Hence, f(x) has the form

    f(x) = a%2Asin%28x%2F2%29,  where real number "a" is the amplitude of f(x).


Next,  we are given  f%28pi%2F4%29 = 4.  It means   a%2Asin%282%2A%28pi%2F4%29%29 = 4,  or  a%2Asin%28pi%2F2%29 = 4.


Since  sin%28pi%2F2%29 = 1,  it gives us  a = 4.


It implies, due to the problem description, that the amplitude of  g(x)  is  2 :  b = 2.


Thus g(x) has the form

     g(x) = 2%2Asin%28x%29.    ANSWER


My other lessons in this site on plotting and analyzing functions are
    - Finding x-intercepts and y-intercepts
    - Compressing and stretching graphs
    - HOW TO PLOT transformed functions
    - HOW TO write functions for transformed plots
    - HOW TO PLOT transformed periodic trigonometry functions
    - Analyzing periodic trigonometric functions for the amplitude, the period, vertical and horizontal shifts
    - Do not fall into a TRAP when analyzing problems on trigonometric functions
    - The domain and the range of transformed functions
    - Write a function which is a result of given transformations of the parent function
    - Describe transformations from the given parent function to final function
    - Constructing a function based on its given properties
    - Finding inverse functions
    - Miscellaneous problems on plots of functions
    - Given a point on a plot of a function, find the corresponding point on the plot of transformed function
    - Special advanced problems on finding the domain of functions
    - Special advanced problems on finding the range of functions
    - OVERVIEW of lessons on plotting and analyzing functions

Use this file/link  ALGEBRA-I - YOUR ONLINE TEXTBOOK  to navigate over all topics and lessons of the online textbook  ALGEBRA-I.

Use this file/link  ALGEBRA-II - YOUR ONLINE TEXTBOOK  to navigate over all topics and lessons of the online textbook  ALGEBRA-II.


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