# What does a greek psi mean in this expression

#### Knotilis

Can anybody point me to a math topic dealing with expressions like this:

if a (psi) b = a - 2b ...

where (psi) is the greek letter psi, the trident

#### romsek

MHF Helper
it looks like they are just treating $\psi$ as an operator, much like "+" or $\div$

Like they say

$a ~\psi~ b = a - 2b$

so for example

$5~ \psi ~17 = 5 - 2(17) = -29$

#### Knotilis

My son ran into this on a standardized test. I have taken lots of math, but the notation is new to me. The question reads,
if a (psi) b = a^2 -2b , which yields the largest value?
a) 3 (psi) 4
b) 3 (psi) 5
c) 4 (psi) 2
d) 5 (psi) 7

From this it's clear that only the expression to the right of the = can be evaluated, because none of the values provided are equal if you treat it as an equation where b = a^2 - 2b

So my guess is that somebody just wanted to use a fancy greek letter, when it would have been simpler to say c = a^2 - 2b so which (a,b) pair yields the largest c?

#### romsek

MHF Helper
My son ran into this on a standardized test. I have taken lots of math, but the notation is new to me. The question reads,
if a (psi) b = a^2 -2b , which yields the largest value?
a) 3 (psi) 4
b) 3 (psi) 5
c) 4 (psi) 2
d) 5 (psi) 7

From this it's clear that only the expression to the right of the = can be evaluated, because none of the values provided are equal if you treat it as an equation where b = a^2 - 2b

So my guess is that somebody just wanted to use a fancy greek letter, when it would have been simpler to say c = a^2 - 2b so which (a,b) pair yields the largest c?
kinda, but they seem to want to get the idea of operators across.

Operators get more complicated to the point that they don't seem pointless
and actually the use of operators results in some very elegant mathematics
that is actually useful stuff in quantum mechanics.

Whatever designed quantum mechanics appreciated the use of operators.

Last edited:

#### Cervesa

Here's another example of an algebraic operator type question

#### Knotilis

I have studied a few operators, so I am familiar with the idea.

Psi *could* be an operator, but if so I would expect it to read &(a,b) or something, where & is (psi). If its an operator the notation is stupid, only suitable for 2 variables.

Thanks for taking time to comment though.

#### Knotilis

Yeah, I believe you're right. It's an operator. I still say the notation is lame.

#### Plato

MHF Helper
Yeah, I believe you're right. It's an operator. I still say the notation is lame.
I have no idea what test your son was taking, but as someone who once was an editor for such tests this is my take.
I can understand how an uninformed amateur may well call this question lame.
However, the question is testing the test taker's ability to understand abstract ideas.
Frankly to that end, I find this question possibly quite effective.
Now i suspect your son may not have found it doable, therefore your objection.
If that is the case then you now know where he needs help.

#### Knotilis

Plato, why did you post? The problem was solved. You only succeeded in stooping to insults, and that demeans you and you alone. How exactly are you helping?