根式問題,,,,,,...........

Although
7^2 = 49 and (-7)^2 = 49

√49=7 only.

This is because the symbol "√ " means "positive square root"

How about -7?
-7 = -√49

Furthermore, in solving equations with radical signs,
we have to reject the answer √x = n. where n is any negative number.
Because a positive square root is never a negative number.
eg:

x - √x - 12 = 0
(√x - 4)(√x + 3) = 0
√x = 4　or　√x = -3 (rejected)
x = 16 only.

2007-08-06 17:22:31 補充：
Plus, eg.x^2 = 49x = √49　or　x = -√49　------ This step, so we can generate:x = 7 　or　x = -7But not :x = √49x = 7　(or　x = -7 ----- This part can't be generated by √49)

ya you are right

Right!Right!

對

因為負負得正,正正都得正