Jawabanmu

2014-06-14T11:44:35+07:00
A² + b² + c² = 756
b² + bc + c² = 756
.
a + b + c = 18
b + c = 18 -a
(b+c)² = (18-a)²
b² + 2bc + c² = 324 + a² - 36a
b² + 2bc + c² = 324 + bc - 36a
b² + bc + c² = 324 - 36a
756 = 324 - 36a
-36a = 756 - 324
-36a  = 432
a = -12
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