Help with inverse functions and things?

chadsobey

New member
Joined
Sep 23, 2010
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I need help finding the inverse of this function:
f(n) = 3-1/2n

I know I need to set it to y and solve for it but where do I start?
Do i move the 3 over to the other side or what?

Also, I worked out (27x^6)^5/3 and got 243x^6 as my final answer.
But the problem after that is 240=-3+(n=3)^5/4 and -16=-4-4m^1/4 how do I work these out?
 


I'm thinking that your typing might be missing some grouping symbols.

You typed:

f(n) = 3-1/2n

This typing means:

\(\displaystyle f(n) = 3 - \frac{1}{2} \cdot n\)

If you mean:

\(\displaystyle f(n) = 3 - \frac{1}{2n}\)

then it must be typed like this:

f(n) = 3 - 1/(2n)

Note the grouping symbols around 2n. They indicate that the denominator is 2n, not 2.

Please clarify your typing.

Likewise, you typed:

(27x^6)^5/3

This typing means:

\(\displaystyle \frac{(27x^6)^5}{3}\)

If the outer exponent is supposed to be 5/3, like this:

\(\displaystyle (27x^6)^{5/3}\)

then you must type it like so:

(27x^6)^(5/3)

Note the grouping symbols around 5/3. They indicate that the outer exponent is 5/3.

Please clarify your typing.

You typed:

240=-3+(n=3)^5/4

No equation has more than one equal sign. Also, is 5/4 an exponent, or is 4 the denominator in a ratio?

Please correct your typing.

Here's how to find the inverse of the linear function f(n), as posted.

f(n) = 3 - 1/2 n

Step 1: Write y instead of f(n)

y = 3 - 1/2 n

Step 2: Switch the n and y variables

n = 3 - 1/2 y

Step 3: Solve for y

n - 3 = 3 - 3 - 1/2 y

n - 3 = -1/2 y

(-2)(n - 3) = (-2)(-1/2 y)

-2n + 6 = y

Step 4: Write y as f-inverse

f[sup:vm9kj1c9]-1[/sup:vm9kj1c9](n) = -2n + 6

Step 5: Check by graphing both f(n) and its inverse, and look for symmetry, OR input the inverse expression -2n + 6 into y = f(n) and verify that it simplifies to y = y.


When you fix your typing, please try to show some work, too. That helps tutors see your mistakes or where you've gone astray.

MY EDIT: Inserted missing negative sign, in my work
 
chadsobey said:
-16=-4-4m^1/4

On this one, I feel safe assuming that 1/4 is an exponent, since it's standard to not write m^1 for m.

You should type grouping symbols around this exponent, anyway.

-16 = -4 - 4m^(1/4)

Start by isolating m^(1/4) on one side. Can you do that part?

You should arrive at:

m^(1/4) = 3

To solve for m, raise both sides to the fourth power and simplify using this property of exponents:

[m^(a)]^b = m^(a*b)

In other words, when one power is raised to another power, multiply the exponents together.

Please show your work, if you need more help with this one.

 
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