Polar form of a vector.

[firemath]

Here is the problem:

Convert 2+2i to polar form. Round magnitude to 1 d. p.
Write answer in McisX form.

So I used the Pythagorean theorem to find the magnitude, and got 2.828 (which I rounded to 2.8)
Then, obviously the angle of the vector is 45 degrees (because the legs are both the same length).

My answer: 2.8cis45.
The automated grading system marked it wrong.

 

[Romsek]

what happens if you use \(\displaystyle 2\sqrt{2}cis45\)

or maybe \(\displaystyle 2\sqrt{2}cis\dfrac{\pi}{4}\) ?

 

[firemath]

what happens if you use \(\displaystyle 2\sqrt{2}cis45\)

or maybe \(\displaystyle 2\sqrt{2}cis\dfrac{\pi}{4}\) ?

Radicals aren't allowed in this case.

 

[MarkFL]

Try:

4 cis(45)

 

[Steven G]

Try:

4 cis(45)

Mark,
Why 4?
Steve

 

[Steven G]

Here is the problem:

Convert 2+2i to polar form. Round magnitude to 1 d. p.
Write answer in McisX form.

So I used the Pythagorean theorem to find the magnitude, and got 2.828 (which I rounded to 2.8)
Then, obviously the angle of the vector is 45 degrees (because the legs are both the same length).

My answer: 2.8cis45.
The automated grading system marked it wrong.

Then try 2.8cis(pi/4)

 

[Dr.Peterson]

Does the system (or the associated textbook) provide no examples (of answers to similar questions) from which you could determine the expected format?

Somewhere you need to be told whether degrees or radians are assumed, and perhaps other details of the formatting, such as whether parentheses are allowed or required. Can you show a screen print of the problem, and of any instruction on the topic?

 

[firemath]

Every time I enter a wrong answer, it takes away credit, so I can't go guessing.

 

[Dr.Peterson]

That's why they can't make you guess. If there's no information telling you how to enter the answer, contact your instructor and find out.

Systems I've worked with always tell you exactly how to format your answer (sometimes a little cryptically), and may provide a way to ask for help (and maybe ask them to override the system's grades).

 

[firemath]

M and X are both supposed to be decimals.

 

[Steven G]

M and X are both supposed to be decimals.

Your initial post never said that X must be a decimal number (to how many places?)!
So write pi/4 as a decimal. Problem solved.

 

[firemath]

Your initial post never said that X must be a decimal number (to how many places?)!
So write pi/4 as a decimal. Problem solved.

Duh. Sorry.

 

[MarkFL]

Mark,
Why 4?
Steve

Because I had a brain fart.

 

[Dr.Peterson]

Duh. Sorry.

Yet another example of the reason we say:

Post the complete text of the exercise. This would include the full statement of the exercise including the instructions, so the tutors will know what you're working on. Typing exercises word-for-word also helps us identify possible mistakes in class materials. If there's a graphic or table or some other non-textual information necessary, please include a detailed description. You may upload images to our server.​

 

[Steven G]

Because I had a brain fart.

Oh OK, I just thought I was missing something.