# evaluate expressions with sets

• Mar 8th 2010, 10:02 PM
ruben22
evaluate expressions with sets
Im stuck on this 2 problems.. help plz!

1.) P = {x E N/x^2 -9=0}

2.) F = {x E Q / (3x-4)(x-√2)=0}

Thank you! I'll appreciate it
• Mar 9th 2010, 12:37 AM
earboth
Quote:

Originally Posted by ruben22
Im stuck on this 2 problems.. help plz!

1.) P = {x E N/x^2 -9=0}

2.) F = {x E Q / (3x-4)(x-√2)=0}

Thank you! I'll appreciate it

1. Solve the given equations.

2. Afterwards check if the solutions belong to the given domain.

3. An example:

$\displaystyle L=\{y \in \mathbb{N}|(2y-5)(y-\sqrt{3})(y^2-1)=0\}$

A product equals zero if one of the factors equals zero:

$\displaystyle \begin{array}{ccc}2y-5=0&y-\sqrt{3}=0&y^2-1=0 \\ y=\frac52&y=\sqrt{3}&y=1\vee y=-1 \end{array}$

As you easily can see only y = 1 is a valid solution. Thus

$\displaystyle L=\{1\}$
• Mar 9th 2010, 12:56 AM
ruben22
That's my problem...I don't know how to use this theory on the problems i was given. I'm not that good at mad :-s