This section gives guidance on the procedure, syntax, etc of answering questions in edX.

Answering Homework Questions

What's on a question page?

1. Title/Points: There's a title at the top telling you the name of the question and how many points the question is worth.
2. Text and (sometimes) images describing the question(s). Note that a single question page may require an answer to multiple sub-questions.
3. A section for your answers. This can be either multiple choice with radio buttons (small circles), multiple choice with a pull-down menu, a box to enter a number, or a box to enter an equation. You can tell the difference between the last two because the former is just a single box while the latter has an additional grey box below it.
4. A "Check" or "Final Check" button and (sometimes) a "Save" button.
5. If the number of times you can answer a question is limited, there will be text next to the buttons listed in item 4 indicating how many times you can answer and how many of those attempts you have used. If you have *only one* chance left, the "Check" button changes to "Final Check".

What's the difference between entering answers and submitting answers:

{#EntSubDiff}

Entering an answer means selecting one of the multiple choice options or typing something into a box. Submitting an answer means telling the system that you have finished entering all of your answers by clicking "Check" (or "Final Check" if you have only one attempt left).

How do I enter my answer?

1. Radio buttons (small circles with numbers or text next to them): Click on the appropriate radio button. To change your answer, click on a different botton. To "erase" your choice and start over, you need to open some other page.
2. Pull-down menu: Click-and-hold on the blue box with up/down arrows, move to the answer you want, and release the mouse button.
3. Number boxes: If there is no additional grey box below the answer box, you can enter a number or a numerical formula, for example (1/2) * 9.81 * 2.5^(-2) , with no blank spaces and no letters for units. The number is assumed to be in the units listed in the question text. Note that you can also use scientific notation, for example 6.67*10^(-11), but note the use of () for the exponent! The system also recognizes "pi". The computer grading algorithm does not know about significant figures so you don't need to worry. Make sure to include enough that your answer is correct to a few %. Note that in many cases, combining two answers which are correct to the required precision (~few %) will not necessarily give a new answer to the required precision (for example, subtracting two big numbers to get one small one).
Do not use a comma for decimals, use a full stop - 3.142, not 3,142
4. Formula boxes: If there is an additional grey box below the answer box, the program might expect a formula or it *might* expect a number, for example 0. Type in the formula for the answer. The system also recognizes "pi". The grey box underneath the answer box will show how the program is interpreting what you have typed. There is more information on how to correctly type in formulas [here](#Syntax).
5. Drag and drop: If you see a formula with things missing and options to fill the missing pieces below, simply drag the correct pieces into place to input your answer.

How do I submit my answer?

You do this by clicking the "Check" or "Final Check" button.

Warning: You must enter your responses to all of the sub-questions first, before submitting your answer (but see the next topic for exceptions to this rule).

How do I save my answer?

If you see a "Save" button, you can use that. When you come back to the page, whatever answers you already entered will still be there. If you don't see a "Save" button, your one option, is to use up one of your attempts by selecting "Check". This is obviously *not* a good choice if you only have one attempt left. But, if you have many (or unlimited) chances, the only down side is seeing the ugly red Xs on the ones you have not answered. When you return to the page, what you have *submitted* already will still be there.
Other options include leaving your browser open and hibernating your machine for the time being or copying your answers into a text file and saving that someplace.

How many times can I answer a question?

See item 5 under "What's on a question page" [above](#QP).

How to Enter Formulas

You can type in formulas exactly as you would enter them into a computer program. However, there are a number of very strict requirements. We strongly encourage you to use the [Example Entry Problem](/courses/MITx/8.EFTx/3T2014/courseware/intro/hw0/) to get experience with the different types of answers.

1. No blank spaces are allowed anywhere in your formula.
2. You must use the multiplication sign ( * ) between every term you are multiplying together, including numbers. The program does not know that Qq means multiply Q times q and it does not know that (2x+1)(2x+2) means myltiply (2x+1) times (2x+2). It does *not* even know that 2x means 2 times x.
3. Your left ( and right ) parentheses must match exactly. Count them carefully and pay close attention to the display of the formula in the grey box below your answer to see if you are getting what you intend.
* One helpful technique is to enter the ( ) first and then type the variables inside them.
4. Use the caret ^ for powers. For powers of variables with subscripts, () will help, for example (R_1)^2, not R_1^2. For more complicated exponents, use more (), for example R^(3/2).
5. Arguments of functions must always be in (), for example sin(x+c*t).
6. Subscripts are entered using the underscore (_) character, for example q_1. No formulas will require superscripts.
7. You will be told how to type specialty characters like Greek letters.
8. The constant pi can be entered as "pi". It is preferable *not* put in a number like 3.14.
9. Be careful to use Upper or lower case letters correctly.
10. You can only use ( ), no curly { } or square \[ ] brackets allowed.
11. Use sqrt( ) for square root and ln( ) for the natural logarithm.
12. You *can* combine numerical factors (for example sqrt(1/3)=0.577350) into your formula but be careful to include *lots* of decimals. Unlike entering purely numerical answers, formula answers need to be *very* precise.
13. You may use trigonometric functions for numerical answers, e.g. sin(pi/2). Beware that the argument of the trigonometric functions must be in radians, not in degrees.

Error Messages

Note that if a question has multiple sub-questions, you will only get an error message for the first one in the list which the system cannot understand. You will not be told which answers are right or wrong until all answers are in correct format.

* Invalid input: could not interpret '15 N/C' as a number: This one is pretty obvious. When you have an answer box with no grey box underneath it, only a single number or numerical formula is allowed. No letters are allowed. For scientific notation, the exponent must be in (), not {}.

* Invalid input: XXX not permitted in answer: Where "XXX" is one of the symbols you included in your answer. This is really a *hint* since it means that the correct answer does not include "XXX" anywhere!

* Invalid input: Could not parse BlahBlahBlah as a formula: This means that there is a mathematical error in your entry. Perhaps you did not match your parentheses () correctly. Look very carefully at what appears in the grey box underneath your answer to see if it looks correct.

How can I see the right answers?

For the lecture questions, after you have submitted your answer (only one try), you should see a "show answer" button. A show answer button on other graded elements will appear only after you have gotten it correct or exhausted your number of attempts. Most of the homework will have written solutions as well as just the answers.