Question

What is the function where it has a maximum point at (pi, 6) and a minimum point at (-3pi/4, 2). Find the function. Give an exact expression.

Answer 1

Answer:

f(x) = 2*cos(4*x) + 4

Step-by-step explanation:

This is obviusly a sinusoidal function, which can be written as:

f(x) = A*cos( w*x ) + M

Where:

A = amplitude

w = angular frequency

M = midline.

Remember that the maximum of a cosine

cos(x) = 1, when x = (2*n)*pi      (for any integer n)

And the minimum is at:

cos(x) = -1, when x = (2*m + 1)*pi    (for any integer m)

Whit this in mind, we know that we have a maximum when:

x = pi

then we want:

w*pi = (2*n)*pi

and a minimum at:

x = -3*pi/4

Then we want

w*(-3*pi/4) = (2*m + 1)*pi

In the minimum case, we have a "4" in the denominator that is kinda unfortunate, so we woud want to take w = 4 in order to remove it, and this will work really well for wath we want, because:

w*pi = 4*pi = (2*2)*pi     (here we have n = 2)

w*(-3*pi/4) = 4*(-3*pi/4) = -3*pi = (2*-2 + 1)*pi   (here we have m = -2)

Then we can take w = 4.

So the function is something like:

f(x) = A*cos(4*x) + M

The amplitude is equal to half of the difference between the maximum and the minimum values of y.

The maximum is:

y = 6

the minimum is:

y = 2

Half of the difference is:

A = (6 - 2)/2 = 2

A = 2

Then our function is:

f(x) = 2*cos(4*x) + M

The value of the midline is equal to the maximum minus the value of the amplitude (or the minimum plus the value of the amplitude)

M = Maximum - A =  6 - 2 = 4

M = Minimum + A =  2 + 2 = 4

Then the function is:

f(x) = 2*cos(4*x) + 4