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Moving left uses plus inside the function argument because horizontal translations modify the input variable. To shift the graph left by $h$ units, you must replace $x$ with $x+h$ so that the function evaluates the original input at a point $h$ units to the right, effectively moving the graph left.

Conditions: The transformation is a horizontal translation of the graph of $y=f(x)$.; The shift amount is a positive constant.

Moving left uses plus inside the function argument because horizontal translations modify the input variable. To shift the graph left by $h$ units, you must replace $x$ with $x+h$ so that the function evaluates the original input at a point $h$ units to the right, effectively moving the graph left.

Conditions: The transformation is a horizontal translation of the graph of $y=f(x)$.; The shift amount is a positive constant.