唔識做功課35

Note:
y is a function of x if
for every x in the domain (the set of possible values of x),
there is ONE AND ONLY ONE corresponding value of y.

Determine whether y is a function of x
1. y² = x² - 1

Ans: No
For some given value of x, such as x = 4, we can calculate two different values of y.
When x = 4, y² = 4² - 1 = 16 - 1 = 15
y = √15 or -√15.


2. y = √(x - 3) (where x ≧ 3)

Ans: Yes
For every value of x ≧ 3, there is ONE and ONLY ONE value of y, because y can be calculated uniquely according to the formula given:
y = √(x - 3).