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This problem seems overwhelming, but let's take this problem one piece at a time.

 

Instead of trying to wrap our heads around f(f(x))=3, we should instead ponder a far easier question. For what values of x does f(x)=3? Well, let's investigate, shall we?

 

f(x) is defined as a piecewise function, so we must more or less treat it as two separate functions and ensure that our answers lie within the restrictions.

 

2x5=32x=8x1=443 x+5=3x=2x2=22<3 I placed checkmarks around both proposed solutions because they respect the boundaries given by the original piecewise function.

 

f(x1)=3 and f(x2)=3. Let and solvef(x)=x1 or f(x)=x2to determine the number of solutions to f(f(x))=3.

 

f(f(x))=3f(x1)=3f(x)=x1f(x)=4 f(f(x))=3f(x2)=3f(x)=x2f(x)=2 Let's find all the values for x that satisfy these two equations. This will require 4 equations in total.
2x5=42x=9x11=92923 x+5=4x=1x12=11<3

 

2x5=22x=7x=72723 x+5=2x=3x=333Invalid solution

 

 

 

Through all this algebra, we have determined that there are 3 values of x for which f(f(x))=3.

Feb 4, 2021

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