I thought I knew the concept of square root that in Gre, ‘square root 4 is only 2.’

So I thought ‘y’ in the below question is only 8, but the answer is D because it can be 8 or -8. Is it because of y^2?

Could anyone please explain what I missed in the concept?

Thank you.

This is just ETS testing if you actually read the whole square/square-root rule… **Square root of anything is only positive** in GRE. But that’s already given, that the square root of something is equal to a **positive** 8.

But the question here is what all can you put under that square root to get the positive 8.

If you’re still confused let me know I’ll try to elaborate more.

yes y can be +8 or -8 since y² = 64. quadratic equations have 2 roots.