Posted by Soroban on September 11, 2002 at 13:50:38:
In Reply to: Finding formula for inverse function (Please Help!) posted by Larry H on September 11, 2002 at 13:23:58:
: Hello, I hope someone can help me with this.
First, I'd let y = f(x). It makes for neater algebra.
: I have to find the formula for the inverse function.
: I get x= (-2*f(x)-1)/(s*f(x)-3), but it is wrong.
This would be: x = (-2y-1)/(2y-3)
I assume that "s" is a "2".
We have: y = (1 + 3x)/(2 - 2x)
: I divided both sides by (2-2x)
You meant "multiplied", of course.
y(2 - 2x) = 1 + 3x
: I distributed
2y - 2xy = 1 + 3x
: I isolated for x terms
-2xy - 3x = 1 - 2y
: I factored out x
x(-2y - 3) = 1 - 2y
: I divided both sides by coefficient of x
x = (1 - 2y)/(-2y - 3)
Multiply numerator and denominator by -1:
x = (2y - 1)/(2y + 3)
Finally: f-inverse(x) = (2x - 1)/(2x + 3)
: Any ideas what I'm doing wrong?
You seem to have dropped (on inserted) a couple of minus-signs.
It may have happened when you "isolated for x terms".
: Thanks, Larry
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