domain and range question

• Oct 9th 2007, 05:05 PM
kruton
domain and range question
if the paper says: Domain = reals, then isn't the range also {y: y= reals}?

thanks

• Oct 9th 2007, 05:09 PM
Jhevon
Quote:

Originally Posted by kruton
if the paper says: Domain = reals, then isn't the range also {y: y= reals}?

thanks

no. it depends on the question. the domain and the range are two different things, they are not always equal.

for instance, for $\displaystyle y = x^2$, the domain is all real x, but the range is all real y that are greater than or equal to zero. so $\displaystyle dom(y) = ( -\infty, \infty)$ and $\displaystyle ran(y) = [0, \infty)$
• Oct 9th 2007, 05:11 PM
kruton
the function is y=-5-2X

domain = reals

range = y greater than or equal to 0

is that right?

but why can't y be less than zero?
• Oct 9th 2007, 05:14 PM
Jhevon
Quote:

Originally Posted by kruton
the function is y=-5-2X

domain = reals

range = y greater than or equal to 0

is that right?

but why can't y be less than zero?

no. the range is all reals as well. like i said IT DEPENDS ON THE PROBLEM. the answers i gave you before were for y = x^2. this is a line, it is different