SAT Mathematics Practice Test 6

The two numerical expressions in the given equation can be simplified as $\sqrt{9}=3$ and $\sqrt{64}=8$ ,so the equation can be rewritten as $\sqrt{x}=3=8$,or $\sqrt{x}=5$ Squaring both sides of the equation gives $x = 25.$Choice A is incorrect and may result from a misconception about how to square both sides of $\sqrt{x}=5$ to determine the value of x.Choice B is incorrect. The value of $\sqrt{x}$,not x is 5. Choice D is incorrect and represents a misconception about the properties of radicals. While it is true that $55+9=64$, it is not true that $\sqrt{55}+\sqrt{9}=\sqrt{64}$