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Given right triangle ABC with altitude B D drawn to hypotenuse AC. If AD = 44 and DC = 4, what is the length of B D in simplest radical form?

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Answer:

4√11

Explanation:

You want the length of the altitude BD in right triangle ABC if it divides the hypotenuse into segments AD=44 and DC=4.

Similar triangles

The altitude to the hypotenuse in a right triangle divides the figure into similar triangles:

∆ABC ~ ∆BDC ~ ∆ADB

Proportional sides

The ratios of the leg lengths in these triangles are the same, so we have ...

AD/BD = BD/DC . . . . . . . ratio of short leg to long leg

44/BD = BD/4 . . . . . . . . . with given numbers

BD² = 4·44 = 4²·11 . . . . . multiply by 4·BD

BD = 4√11 . . . . . . . . . . . take the square root

The length of BD is 4√11.

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Additional comment

The altitude to the hypotenuse of a right triangle is the geometric mean of the segment lengths of the hypotenuse, as we see above:

BD = √(AD·DC)

There are two other geometric mean relations in this geometry. Each is a direct result of the proportional relation between corresponding sides.

AB = √(AD·AC)

CB = √(CD·CA)

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