f ( x ) = 1 / x - 2
g ( x ) = 4 / x
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( f o g )( x ) = f ( g(x) )
f ( g(x) ) = 1 / g(x) - 2
f ( g(x) ) = 1 / ( 4 / x ) - 2
f ( g(x) ) = x / 4 - 2x
