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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