I used an online math site, to explain quadratic equations. But the thing is, they said that (-4)^2 is 16, but my calculator said -16. Why is that? And also, how does the square root of 40 break down into the square root of 4 and the square root of ten? Does this have to do with GCF's?
Your calculator is wrong.
Enter 4, then press the "change of sign" button (if you have one) to get -4 in the display, and then hit x^2.
If you still get -16, get a better calculator , or call them for tech help. I hope you saved your receipt.
sqrt 40 = sqrt (4*10) = 2 sqrt 10
This has nothing to do with GCF's