If you think my first answer sounds more complicated than you'd prefer, then just draw a right-angled triangle with base=4 and height=8 and Pythagoras says the hypotenuse will be √80. 😛

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Given: Ø = 51°

opposite = 15

Find: sin Ø =

It doesn't matter what else you throw into the picture,

if Ø = 51° then sin Ø always equals 0.777146

🎭 🎭 😎 

You need a line of length √5, and at one end of it draw a perpendicular line of length 4. Join their ends to form the hypotenuse and applying the wisdom of Pythagoras this third line will be of length √80. 😁 😁 😁

But wait! Where do you find that first line of length √5? You must construct it also—as the hypotenuse of a ∆ having base=1 and whose height=2.

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You have a discrete graph if data on one of the axes can take only discrete values, e.g., the count of how many times each side of a dice turns up when you roll it a few dozen times. Your horiz axis needs discrete numbers 1-6 and it doesn't make sense to want to interpolate to find how many times the graph predicts that the number 2.8 would come up. So you don't join the plotted points because a continuous plot tacitly invites readers to interpolate between the plotted points.

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You can write this in its equivalent form:

\({176.53 \over {a}}\ =\ 10\)

Now can you solve for 'a'?

If I correctly understand what you have in mind, then try replacing each decimal with its equivalent common fraction, e.g., instead of 3.86 you can write \({386} \over {100}\)

Does that help?

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e is a mathematical constant, approximately 2.71828

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It is easier to write e than 2.71828 😜

👉 Your calculator probably has this number already stored in it, look for the e button. A scientific calculator has a button with the power function, e to-the-power x, and it's this button you can use to calculate y in your formula once you know a value for x.

Badinage

That isn't a recursive formula, though you could arrange it as one, e.g., 

\(V_{n+1}\ =\ \frac 3 4 V_n \)

What type of calculator are you using?

The "mean" is just the average. 

$$log_3\ 81\ =\ log_3\ (3^4)\ =\ 4$$