Which of the following is NOT a solution of the equation y 2 =x+x+x+x?

This equation can simplify to $${{\mathtt{y}}}^{{\mathtt{2}}} = {\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}$$

First, get y by itself: $${\mathtt{y}} = {\sqrt{{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}}}$$

Now set y to 0 and solve 

$${\mathtt{0}} = {\sqrt{{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}}}$$

$${\mathtt{x}} = {\mathtt{0}}$$

So you found that (0,0) is one solution - that is certainly correct:)