# Truth value of the statement

• Sep 30th 2008, 05:50 AM
captainjapan
Truth value of the statement
P(x,y) means "x + 2y = xy", where x and y are integers.
Determine the truth value of the statement.

(a) P(1,-1).
(b) P(0, 0).
(c) ∃y P(3, y).
(d) ∀x ∃y P(x, y).
(e) ∃x ∀y P(x, y).
(f) ∀y ∃x P(x, y).
(g) ∃y ∀x P(x, y).
(h) CS173 Discrete Mathematical Structures ¬CS173 Discrete Mathematical Structures ∀x CS173 Discrete Mathematical Structures ∃y CS173 Discrete Mathematical Structures ¬P(x, y).
• Sep 30th 2008, 07:59 AM
Soroban
Hello, captainjapan!

I'll have to make some guesses . . .

Quote:

$P(x,y)$ means " $x + 2y \:=\: xy$", where $x$ and $y$ are integers.

Determine the truth value of the statements.

$(a)\;P(1,-1)$

We have: . $(1) + 2(-1) \:=\:(1)(-1)$ . . . True

Quote:

$(b)\;P(0, 0)$
We have: . $(0) + 2(0) \:=\:(0)(0)$ . . . True

Quote:

$(c)\;\exists y\: P(3, y)$
We have:
. . There exists $y$ such that: . $(3) + 2(y) \:=\:(3)(y)$ . . . True

Quote:

$(d)\;\forall x\:\forall y\:P(x, y)$
This says: $x + 2y \:=\:xy$ for all $x$ and $y$ . . . not true.

Quote:

$(e)\;\exists x\:\exists y\:P(x, y)$
There is an $x$ and $y$ such that: $x + 2y \:=\:xy$ . . . True
[See parts (a) and (b).]

Quote:

$(f)\;\forall y\:\exists x\: P(x, y)$
This says: for any $y$, there is an integer $x$ such that $x + 2y \:=\:xy$ . . . not true.

If $y = 4$, we have: . $x + 8 \:=\:4x\quad\Rightarrow\quad x = \frac{8}{3}$ ... not an integer.

Quote:

$(g)\;\exists y\:\forall x\:P(x, y)$

This says: for any $x$, there is an integer $y$ such that $x + 2y \:=\:xy$ . . . not true.

If $x = 5$, we have: . $5 + 2y \:=