D C
| /
| /
| /
|/__________B
A
<BAC + <CAD = 90°
<BAC = (5/4) × <CAD
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Inlocuim pe <BAC din ecuatia a doua, in prima ecuatie.
(5/4) × <CAD + <CAD = 90°
<CAD × [(5/4) + 1] = 90°
<CAD × (9/4) = 90°
<CAD = 90 × 4 / 9 = 10 × 4 = 40°
<BAC = 90° - 40 = 50°