å¨ä¸è§å½¢abcä¸ï¼å·²ç¥sinCï¼2sinA-sinC=b^2-a^2-c^2ï¼c^2-a^2-b^2
ï¼1ï¼æ±è§B大å°
ï¼2ï¼è®¾T=sin^2A sin^2B sin^2Cæ±Tçåå¼èå´
解ï¼
sinC/(2sinA-sinC) = (b2-a2-c2)ï¼(c2-a2-b2)
c/(2a-c) = (b2-a2-c2)ï¼(c2-a2-b2)
(2a-c)/c = (c2-a2-b2)ï¼(b2-a2-c2)
(2a-c)/c +1 = (c2-a2-b2)ï¼(b2-a2-c2) +1
2a/c = [(c2-a2-b2)+(b2-a2-c2)]ï¼(b2-a2-c2)
2a/c = -2a2 / (b2-a2-c2)
a2+c2-b2 = ac
2accosB=ac
cosB=1/2
B= 60°
T
= sin2A+sin2B+sin2C
= 3
.
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