1.【cos(A-B)+1】cosB-sin(A-B)sinB+cos(π-B)=-3/5
cos(A-B)cosB-sin(A-B)sinB=-3/5
cos(A-B+B)=-3/5
cosA=-3/5
2.sinA=4/5 a/sinA=b/sinB sinB=√2/2 cosB=√2/2
sinC=sin(π-(A+B))=sin(A+B)=√2/10
c=1
→BA在→BC方向上的投影=c cosB=√2/2
1.【cos(A-B)+1】cosB-sin(A-B)sinB+cos(π-B)=-3/5
cos(A-B)cosB-sin(A-B)sinB=-3/5
cos(A-B+B)=-3/5
cosA=-3/5
2.sinA=4/5 a/sinA=b/sinB sinB=√2/2 cosB=√2/2
sinC=sin(π-(A+B))=sin(A+B)=√2/10
c=1
→BA在→BC方向上的投影=c cosB=√2/2