SOLUTION: f(x) is a function such that f(1)=2, f(4)=3, f(7)=4, f^-1(x) is the inverse of f(x),what is f^-1(f^-1(3))? Thank you.

Algebra ->  Rational-functions -> SOLUTION: f(x) is a function such that f(1)=2, f(4)=3, f(7)=4, f^-1(x) is the inverse of f(x),what is f^-1(f^-1(3))? Thank you.       Log On


   



Question 919877: f(x) is a function such that f(1)=2, f(4)=3, f(7)=4, f^-1(x) is the inverse of f(x),what is f^-1(f^-1(3))? Thank you.
Found 2 solutions by MathLover1, josgarithmetic:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

f%28x%29=y
f%281%29=2 => means if x=1 then y=2;it's point (1,2)
f%284%29=3 => means if x=4 then y=3;it's point (4,3)
f%287%29=4=> means if x=7 then y=4;it's point (7,42)
use these points to find what f%28x%29 is equal to
Solved by pluggable solver: Find the equation of line going through points
hahaWe are trying to find equation of form y=ax+b, where a is slope, and b is intercept, which passes through points (x1, y1) = (1, 2) and (x2, y2) = (7, 4).
Slope a is .
Intercept is found from equation a%2Ax%5B1%5D%2Bb+=+y%5B1%5D, or 0.333333333333333%2A1+%2Bb+=+1.66666666666667. From that,
intercept b is b=y%5B1%5D-a%2Ax%5B1%5D, or b=2-0.333333333333333%2A1+=+1.66666666666667.

y=(0.333333333333333)x + (1.66666666666667)

Your graph:




so, y=%280.333333333333333%29x+%2B+%281.66666666666667%29 or
y=%281%2F3%29x+%2B+1.66666666666667
then inverse f%5E%28-1%29%28x%29 will be:
y=%281%2F3%29x+%2B+1.66666666666667 ...swap x and y
x=%281%2F3%29y+%2B+1.66666666666667
x-1.66666666666667=%281%2F3%29y+
%28x-1.66666666666667%29%2F%281%2F3%29=y+
3%28x-1.66666666666667%29=y+
3x-5.00000000000001=y+
y=3x-5+
or
f%5E%28-1%29%28x%29=3x-5

what is f%5E-1%28f%5E-1%283%29%29: first find f%5E-1%283%29=3%2A3-5=9-5=4 and plug it in
f%5E-1%28f%5E-1%283%29%29=f%5E-1%284%29=3%2A4-5=12-5=7

Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
f^-1(2)=1, f^-1(3)=4, f^-1(4)=7.

Start with the inside of your unknown expression and work outward.


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f%5E-1%28f%5E-1%283%29%29
f%5E-1%284%29
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