由余弦定理 a²=b²+c²-2bc*cosA ∴16=4+c²+c c²+c-12=0 c=3
cosA=-1/4 ∴sinA=√(1-cos²A) =√15/4
由正弦定理 a/sinA =c/sinC 得4/(√15/4 )=3/sinC sinC=3√15/16
已知:在三角形ABC中,若a=4,b=2,cosA=-1/4,求c,sinC的值
已知:在三角形ABC中,若a=4,b=2,cosA=-1/4,求c,sinC的值
数学人气:276 ℃时间:2019-10-19 16:48:43
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