CK12 - Geometry

B.Writea similaritystatementfor the triangles.

or equivalent

C.Nameall pairsof congruentangles.

, ,

D. Write equationsstatingthe proportionalside lengthsin the triangles.

or equivalent

IndirectMeasurement

A traditionalapplicationof similartrianglesis to measurelengthsindirectly. The lengthto be measuredwould
be somefeaturethat was not easilyaccessibleto a person.This lengthmightbe:

• the widthof a river


• the heightof a tall object


• the distanceacrossa lake,canyon,etc.

To measureindirectly, a personwouldset up a pair of similartriangles.The triangleswouldhavethree
knownside lengthsand the unknownlength.Onceit is clearthat the trianglesare similar, the unknown
lengthcan be calculatedusingproportions.

Example 3

Flo wantsto measurethe heightof a windmill.She held a

foot verticalpipe with its basetouchingthe level ground,and the pipe’s shadowwas

feet long.At the sametime,the shadowof the towerwas

feet long.How tall is the tower?

Drawa diagram.