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Crossing Ladders
                                       The Classic Problem in Trigonometry





Step 3:  Ratio of AC and GH

 

We follow the same procedure as in Step 2 to use the Pythagorean Theorem to derive the ratio between AC and GH. 

Triangle CGA

We observe triangle CGA:

 

As described above, according to the Pythagorean Theorem, the square of the hypotenuse equals the square of the base plus the square of the height.  In the triangle CGA above:

CG2 = AC2 + GA2

We know that the value of the line CG is 25, and we can substitute:

252 = AC2 + GA2

and simplify:

AC2 = GA2 - 625

By looking at the diagram above, we notice that the line GA is comprised of the line HA plus the line GH, so be can substitute, in place of GA2 , the value (HA + GH)2 as follows:

AC2 = (HA + GH)2 - 625

Notice that the value of line HA is the same as the value of line OB, and we know that line OB equals 5.  Thus we can substitute for HA with this value:

AC2 = (5 + GH)2 - 625

Further simplifying:

AC2 = (25 + 10GH + GH2) - 625

Simplifying again, we derive the fifth basic equation and complete Step 3:

AC2 = GH2 + 10GH - 600             (5)

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