GMAT Math

sqrt(4) = 2.... sqrt(4) = +,- 2


Simple enough, right? During the course of working practice problems, I have sometimes gotten tripped up with the particular usage, however.

I think I am seeing the light but please tell me if my general rules below are flawed:

1.)

When solving a quadratic for its roots, you should use both positive and negative roots (and check for extraneous roots)
y= x^2-4
x=+,- 2


2.)

When working with functions like y = sqrt(x), using the positive root is sufficient.


I hope I don't look like an idiot for asking this, but I want to make sure I get it so I don't hesitate next time I see these kinds of problems....

If anyone can expand on this and explain why it's ok to use just the positive root sometimes and not others, please do!

If the GMAT puts the number under a sqrt sign then you can assume they only want the positive root - if you are taking the SQRT yourself as is x^2=4 then you have to consider both positive and negative values. Thus your statements are correct becuase in quadratic problems you would be putting the SQRT symbol in.