Write what you mean...
or risk confusion!

Here is a typical problem involving an inclined plane: A block of wood is pulled up along an incline against friction using a string held parallel to the incline.

The equations of interest, written accurately, are:

Don't worry right now if you don't understand how to get the equations; the point of this example is that each and every symbol, bracket, superscript or subscript is important in organizing an equation and in conveying its meaning to the reader (including the person who wrote it!).

Here is what a student wrote on her test paper instead:

Based on the fact that the y subscript is present in the second equation, and on other information on the test paper, I knew she understood the meaning of the subscripts x and y. She omitted the x subscript in the first equation by accident, and went on to calculate and use F_g to get the wrong answer.

The second error is a common one: she wrote an equation and its algebraic rearrangement on the same line, connected by equal signs and with intermediate steps missing. As a result, she calculated (F_g)_y= cos25^o= 0.906 (never using the constants m or g).

Writing physics equations should be done with the same level of care you take in writing a formal essay: you must be clear and concise, and you must proofread your work for accuracy. Unfortunately, this sometimes requires that you first unlearn some bad habits developed in high school-- including the tendency to write equations like you would write a run-on sentence.

I often see these kinds of mistakes: an equation is being rearranged to solve for an unknown (see the tutorial on cross multiplying).

In this example, the negative sign and the fraction were both handled carelessly in the rearrangement, and it was not a good idea to write everything on one line connected by equal signs. See if you can rewrite the steps to come up with the correct answer, which is x= -0.0696 .

Let's look at one more example, and work it out together. The goal is to rearrange this equation to solve for y:

You should write out every step in the algebra until you are proficient at these types of problems. Even then, don't use more than one equal sign in the same step:

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