If it's an exam question, often it has been designed so you'll be able to see one solution by inspection, e.g., try various easy possibilities such as ½, ¼, 1, 2, 3, 5, 10, and their negatives. Once you know one solution, call it k, then use division by (x-k) to end up with a quadratic and solve that using the memorized formula.

If the problem hasn't been designed for easy solution, then I'm afraid you're SOOL.

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You should have added this question to the original thread.

A plate with +++ charges has the higher potential than one with - - -  charges; "higher" means more positive potential.

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$$\textcolor[rgb]{0,0,1}{\mathbf{Yes, 4\ sig\ figs\ is\ the \ best\ you \ can\ do\ because\ that's\ the\ accuracy\ of\ our \ least\ accurate\ data.}}$$

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For the "LN" function rest your mouse on "LOG" or the faint arrows underneath "LOG" and a few extra keys will appear by magic!! 

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$$v_a - v_b = \frac{kQ}{r_a} - \frac{kQ}{r_b}$$

If this is what you wrote, then it's right. (I can't make out what that letter is you wrote where there needs to be Q.)

Cheers.

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Q: > Can anybody tell me what they think is the most important job that needs math is? Hint: so i can avoid that job.

A: IMHO, shopping!!

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Q: cos^-1(-3.48), why is the calculator say invalid argument?

Because -3.48 is way out of range.

cos(x) must be -1 ..... +1, inclusive, so -3.48 is impossible.

cosine can be described the ratio of two sides of

a right-angled triangle, cos = adj/hyp,

and hypotenuse is always the longest side.

This means the ratio |adj/hyp| cannot exceed 1.

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negative subtract a positive?

Let's try a few concrete examples:

-7 - +2 = -9

-7 - +10 = -17

-7 - +7 = -14

So we can generalize: the answer is negative.

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Melody wrote:

> You made a little mistake at the end Badinage :/

Oops, so I did. I appreciate your correction, Melody.