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Right Triangles and Trigonometry Videos 37 videos
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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?
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.
Full Transcript
- 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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