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Explanation:
The point (0,0) means x = 0 and y = 0 pair up together.
Recall that any point is always of the form (x,y).
If we plug x = 0 and y = 0 into the equation, we end up with,
y = 3x
0 = 3*0
0 = 0
We get the same thing on both sides, so we have a true equation.
Since we have a true equation, we've shown that (0,0) is a solution.
Visually this indicates (0,0) is on the line y = 3x. Put another way, the line y = 3x goes through the origin.
