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设Haåa为bç¸é»çxåcç¸é»ça-x两é¨å
b^2-x^2=c^2-(a-x)^2
b^2-c^2=x^2-(a-x)^2
=2ax-a^2
(a^2+b^2-c^2)/2a=x
Ha^2=b^2-x^2=b^2-[(a^2+b^2-c^2)/2a]^2
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cosC=(a^2+b^2-c^2)/2ab
Ha^2==b^2-(bcosC)^2
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