Normal Cartesian functions (y = ...) can be entered into the graph tool with or without the y=.
y = 3x - 7
OR
3x - 7
The graph tool is optimised for normal Cartesian functions. Some of the graph tool's are only available for Cartesian functions.
The graph tool will always attempt to rearrange functions into normal Cartesian functions to ensure that the most options are available.
For example:
3x2 + y = 3x + 2
will be internally rearranged by the graph tool into:
y = (3x(1 - x)) + 2
and all features will be available.
In the diagram above, notice how we entered the function as 3x2 + y = 3x + 2 but the graph tool has rearranged the function when finding the integral.