在三角形ABC中,AC=2,BC=1,cosC=3/4,AB求出为根号2.求sin(2A+C)的值

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b=2,a=1,c=√2
cosC=3/4
sin²C+cos²C=1
0======以下答案可供参考======
供参考答案1:
倾斜角是a则k=tana=(1+3)/(2-m)=4/(2-m)
m0所以a=arctan[4/(2-m)]
m>2,ka=π+arctan[4/(2-m)]
综上mm>2，a=π+arctan[4/(2-m)]
供参考答案2:
(1+1/n)+(1+2/n)+(1+3/n)+¨¨¨+[1+(n-1/n)]
=1+1+……+1+1/n+2/n+……+(n-1)/n
=(n-1)+[1+2+……+(n-1)]/n
=(n-1)+[n(n-1)/2]/n
=(n-1)+(n-1)/2
=(3/2)n-3/2
所以原式=lim(n→∞)(1/n)[(3/2)n-3/2]
=lim(n→∞)[3/2-3/(2n)]
=3/2-0
=3/2