Undefined control sequence \dpi
Undefined control sequence \dpi
Undefined control sequence \dpi




High School Math : How to find the length of the side of a right triangle

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #141 : Plane Geometry

Triangles

Points \dpi{100} \small A, \dpi{100} \small B, and \dpi{100} \small C are collinear (they lie along the same line). \displaystyle \angle ACD = 90^{\circ}\displaystyle \angle CAD=30^{\circ}, \displaystyle \angle CBD=60^{\circ}, \displaystyle \overline{AD}=4

Find the length of segment \overline{BD}\displaystyle \overline{BD}.

Possible Answers:

\frac{4\sqrt{3}}{3}\displaystyle \frac{4\sqrt{3}}{3}

\frac{\sqrt{3}}{2}\displaystyle \frac{\sqrt{3}}{2}

\frac{2\sqrt{3}}{3}\displaystyle \frac{2\sqrt{3}}{3}

2\displaystyle 2

2\sqrt{3}\displaystyle 2\sqrt{3}

Correct answer:

\frac{4\sqrt{3}}{3}\displaystyle \frac{4\sqrt{3}}{3}

Explanation:

The length of segment \overline{BD}\displaystyle \overline{BD} is \frac{4\sqrt{3}}{3}\displaystyle \frac{4\sqrt{3}}{3}

Note that triangles \dpi{100} \small ACD and \dpi{100} \small BCD are both special, 30-60-90 right triangles. Looking specifically at triangle \dpi{100} \small ACD, because we know that segment \overline{AD}\displaystyle \overline{AD} has a length of 4, we can determine that the length of segment \overline{CD}\displaystyle \overline{CD} is 2 using what we know about special right triangles. Then, looking at triangle \dpi{100} \small BCD now, we can use the same rules to determine that segment \overline{BD}\displaystyle \overline{BD} has a length of \frac{4}{\sqrt{3}}\displaystyle \frac{4}{\sqrt{3}}

which simplifies to \frac{4\sqrt{3}}{3}\displaystyle \frac{4\sqrt{3}}{3}.

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