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ACT Math 5.3 Trigonometry 192 Views


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ACT Math: Trigonometry Drill 5, Problem 3. What is the length of side x?

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Transcript

00:02

Here's your shmoop du jour...

00:05

cos(A) = 3/7. What is the length of side x?

00:09

And here are your options...

00:14

Okay, so we know the cosine of angle A...

00:16

and we need to use it to find the length of side x...

00:20

The cosine of an angle is equal to the adjacent side over the hypotenuse.

00:24

If the adjacent side is 3 and the hypotenuse is 7, we can use the Pythagorean theorem to

00:29

solve for the missing leg, x.

00:37

So we can just plug our numbers into this formula,

00:39

Three squared plus x squared equals seven squared.

00:43

9 plus x squared equals 49.

00:49

x squared equals 40.

00:53

x equals the square root of 40.

00:55

The square root of 40 is equal to 2 root 10, and there you have it...

00:59

...option C. That's the way to go.

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