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ACT Math 3.1 Trigonometry 257 Views


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Description:

ACT Math: Trigonometry Drill 3, Problem 1. What is side DE?

Language:
English Language

Transcript

00:02

For a good time, solve this shmoopy question...

00:05

For the right triangle DEF, F = 60° and DF = 10.  What is DE?

00:12

And here are your potential answers...

00:15

OK this problem is really testing one thing and one thing only...

00:18

...whether we recognize that we have a 30-60-90 triangle here.

00:22

But if we do recognize it, then we know that this angle is 90 degrees... F here is 60 degrees...

00:29

and E here is 30 degrees.

00:31

We should know that the ratio of the sides of a 30-60-90 triangle is 1 to square root

00:35

of 3 to 2.

00:36

If we label each side we have 1 here, square root of 3 here and 2 here.

00:43

The question asks for the length of DE; well, we know that DE is to DF as square root of

00:49

3 is to 1...

00:51

DF has a length of 10 and

00:53

the key equation looks like this:

00:55

Square root of 3 over 1 equals DE over 10.

00:59

Cross multiply and we have 10 times square root of 3 equals 1 times DE... or just, uh, DE...

01:05

So the answer is B.

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