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So I would like to figure out how tall a building is and here's what I know. I am standing 200 ft away from the base of the building and from that point I used a range finder and pointed it to the top of the building and got 700 ft. So at 200 ft away, at a angle, the top is 700 ft from me. How could I figure out how tall the building is?

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    Simple application of Pythagora's theorem. – 2017-02-16

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Do you know the Pythagorean theorem? You have two sides of a right triangle. $a^2+b^2=c^2$

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    Yeah I looked that up but I'm doing it wrong. I'm not very good at math. I would like to be able to figure it out but I'm getting some crazy high numbers – 2017-02-16
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    @Matt: without seeing your calculation we can't say what is wrong. You have $a=200, c=700$ – 2017-02-16
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    @Matt You can use the "edit" button to add information to your question. To make the formula $a^2+b^2=c^2$ as in this answer, type `$a^2+b^2=c^2$`. To make $\sqrt{x}$ type `$\sqrt{x}$`. With a little trial and error, watching the preview pane below the edit pane, you should be able to show the formulas and equations you used. – 2017-02-16
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    Is 670 the answer? If not I'll put down what I'm doing, just tight on time at the moment – 2017-02-16
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    I get closer to $671$ – 2017-02-16
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    Yeah you're right. Thanks. – 2017-02-16
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    It is a general point that if the legs of a right triangle are different, the long one is rather close to the hypotenuse. If $b \gt a$ you can write $b=\sqrt{c^2-a^2}=c\sqrt{1-\frac {a^2}{c^2}}\approx c(1-\frac{a^2}{2c^2})$ and the last term is rather small. – 2017-02-16
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$670.82ft$ or $\sqrt(700^2 - 200^2)$ As the comments above tell you, $a^2+b^2=c^2$.

This can easily be rearranged to $\sqrt(c^2-b^2)=a^2$. Here, $a=x$ ,$b=200$ and $c = 700$.