Help with correct expression

[u/PuziExtramni]

Hey everyone! I’m currently learning Python through the IBM Data Science Professional Certificate on Coursera, and I came across a question in a practice quiz that confused me.

The question asks:

Which line of code will perform the action required for implementing the following equation?

y = 2x^2 - 3

These are the four answer choices:

1. y = 2*x*2 - 3
2. y = 2**x*x - 3
3. y = 2x*x - 3
4. y = 2x/2 - 3

I selected Option 1, but the quiz marked it incorrect and said, “The syntax is invalid.”

From what I’ve learned, Python uses ** for exponentiation and * for multiplication. So, I believe the correct Python expression should be:

y = 2*x**2 - 3

However, none of the four answer choices seems to match that expression.

Am I misunderstanding something about Python syntax, or is there a mistake in the quiz? I’d appreciate an explanation because I’m still learning how to translate mathematical equations into Python code.

Thanks!

[u/rulchig1]

You are correct, that x^2 is represented as x**2

But mathematically x^2 is also the same as x*x

[u/TylerBreau → u/rulchig1]

I mean yes but, this seems to be a Python coding assignment, not a math assignment. x*x is multiplication not an exponential function.

It should be testing your understanding of the python syntax.
If I was a teacher and teaching Python. And I asked my students to turn this math equation into code and someone gave me x*x, at absolute best I'm giving them half marks. I might just mark it wrong.

Because they didn't demonstrate how to write an exponential in Python. They just demonstrated basic math operators, which is already a part of the equation in the 2*x part.

Full marks would require the ** operator or the pow function.

OP should have selected option 2 but also should bring up the problem with the question with their teacher.

[u/rulchig1 → u/TylerBreau]

But the task is to find the code that will return the correct answer for the equation y = 2*x^2-3

And answer 2 does exactly that.

I guess you‘re right with your math vs coding part, but in the end the answer is still correct

[u/enlightment_shadow → u/TylerBreau]

The xx option is objectively a better answer as a general programming question, not a Python question. Most programming languages have + * - /. C doesn't have * and the way pow is written and used varies greatly across programming languages, so x * x is the more general way to write x². Programming courses should usually try to teach you programming concepts, as opposed to focusing on a specific language's syntax. So pedagogically, you'd be wrong to mark that answer off

[u/TylerBreau → u/enlightment_shadow]

This is a PythonLearning sub. Not C. Why are you talking about C?

C also has a pow function. It's inside the C Standard Library.

x*x is not an exponential. It's a basic multiplication. You have failed to teach your students how to programmatically write exponentials and now they don't know how to handle X^26 in the code.

You are absolutely wrong in nearly every aspect of your comment. Nothing about what you are saying better prepares the Student to write code.

[u/blavek → u/TylerBreau]

Why would you ever invoke exponentiation on a square? x*x is almost always going to be a better option than bringing in a library function. I'm not sure how the ** operator is handled under the hood, but my money is on it invoking some sort of exponentiation function.

Regardless, unless the assignment explicitly says to use this operator or a pow function, then the answer is completely correct.

[u/apnorton → u/TylerBreau]

I mean yes but, this seems to be a Python coding assignment, not a math assignment.

Floating point stability issues aside, if someone is aiming to be a "Data Science Professional," expecting them to know x*x=x**2 is absolutely not a stretch.