Question

在三角形ABC中,角A,B,C,的对边分别为a,b,c,已知向量M=(a+c,b-c),N=(a-c,b),且M向

Answer 1

(1)∵向量M⊥向量N∴向量M*向量N=0∴(a+c)(a-c)+(b-a)*b=0∴a^2-c^2+b^2-ab=0∴a^2+b^2-c^2=ab∴cosC=(a^2+b^2-c^2)/(2ab)=ab/(2ab)=1/2∴C=π/3.(2)∵△ABC∴A+B+C=π.∵C=π/3∴A+B=2π/3∴B=2π/3-A∴sinB=sin(2...