a=4,b+c=5,根號3乘以sinC-cosC=1
a/sinA=b/sinB=c/sinC
根號3sinC-cosC=2((根號3)/2sinC-1/2cosC)=1
cos(-60)sinC+sin(-60)cosC)=1/2
sin(C-60)=1/2
C-60=30或C-60=150
C=90度或C=210(舍去）
b+c=5
a=4
a^2+b^2-2abcos90=c^2=(5-b)^2
16+b^2=25-10b+b^2
10b-9=0
b=9/10
S=1/2absinC=1/2*4*9/10sin90=2*9/10=9/5如列方程組1、sin²C+cos²C=12、根號3sinC-cosC=1求得C=60°到底是誰算錯數(shù)了？不好意思，算錯了。a=4,b+c=5,根號3乘以sinC-cosC=1a/sinA=b/sinB=c/sinC根號3sinC-cosC=2((根號3)/2sinC-1/2cosC)=1cos(-30)sinC+sin(-30)cosC)=1/2sin(C-30)=1/2C-30=30或C-30=150C=60度或C=180舍去）b+c=5a=4a^2+b^2-2abcos60=c^2=(5-b)^216+b^2-4b=25-10b+b^26b-9=0b=9/6=3/2S=1/2absinC=1/2*4*3/2sin60=3根號3/2