题目:
三角形ABC中角A.B.C所对的边分别为a,b,c且满足csinA=acosC
⑴求角C大小?⑵求√3sinA-cos(B+C)的最大值,并求取得最大值时角A B的大小.
答案:
(1)、在△ABC中
∵csinA=acosC
∴a/sinA=c/cosC
又∵根据正弦定理:a/sinA=c/sinC
∴sinC=cosC
∴∠C=45°
(2)、√3sinA-cos(B+C)
=√3sin(B+C)-cos(B+C)
=2[√3/2*sin(B+C)-1/2*cos(B+C)]
=2sin(B+C-π/6)
=2sin(B+π/4-π/6)
=2sin(B+π/12)
∵∠C=π/4
∴∠A+∠B=3π/4
即0