# ACT Math 3.1 Trigonometry

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

ACT Math | Trigonometry |

ACT Mathematics | Trigonometry |

Foreign Language | Arabic Subtitled Chinese Subtitled Korean Subtitled Spanish Subtitled |

Geometry | Right Triangles and Trigonometry |

Language | English Language |

Product Type | ACT Math |

Trigonometry | Solving right triangles Trigonometric relations in right triangles |

### Transcript

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

and E here is 30 degrees.

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

of 3 to 2.

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

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

3 is to 1...

DF has a length of 10 and

the key equation looks like this:

Square root of 3 over 1 equals DE over 10.

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

So the answer is B.