Question 163289
First, put your function in terms of x and y.
{{{y=3x-1}}}
Now interchange x and y, then solve for y.
{{{highlight(x)=3*highlight(y)-1}}}
{{{3y=x+1}}}
{{{y=(x+1)/3}}}
That's the inverse of the original function.
{{{f^(-1)(x)=(x+1)/3}}}
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{{{y=(x+3)/2x}}}
{{{highlight(x)=(highlight(y)+3)/(2*highlight(y))}}} 
{{{2xy=y+3}}}
{{{2xy-y=3}}}
{{{y(2x-1)=3}}}
{{{y=3/(2x-1)}}}
{{{f^(-1)(x)=3/(2x-1)}}}