Posted by **Mary** on Sunday, November 11, 2012 at 5:03pm.

How would I go about finding the domain and range of 3cos(3x+π) = 4? Thanks

- Precalculus -
**Reiny**, Sunday, November 11, 2012 at 6:06pm
You have given me an equation, not a function

The concept of domain and range applies to functions

was your function

f(x) = 3cos(3x+π) - 4 ?

if so , the domain is any real number

the range is -1 to -7

were you looking for a solution to your equation?

cos(3x+π) = 4/3

BUT, the cosine of anything lies between -1 and 1

so your equation has no solution.

- Precalculus -
**Mary**, Sunday, November 11, 2012 at 6:28pm
The question(s) were as follows:

Given: f(x) = 3cos(3x+π) - 4 (as you thought)

Find:

a) the inverse of F(x)

b) the domain and range of F(x)

c) the domain and range of F -1(x)

I got cos-1[(x-4)/9] - π =y for the inverse, although I'm not sure I did the problem right (I set x to y and y to x and then solved for y).

For cos(3x+π) = 4/3, don't I have to finish solving cos(3x+π) before I decide that there is no solution? I have been doing these and other problems for so long today that I am gettin more confused - not less, lol! Thanks for your help.

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