大哥们！快来解围撒！
由向量a和向量b的坐标知，a*b=0
且向量x垂直于向量y，可知x*y=0
x*y=（a+（t-3)*b）*（-k*a+t*b）=-ka^2+ta*b-(t-3)a*b+t(t-3)b^2
由坐标得|a|^2=4,|b|^2=1,
则x*y=-4k+t(t-3)=0
k=1/4t(t-3)，即k=f(t)=11/4t(t-3)
这是一个二次函数，派差图像开口向上，对称轴是x=3/2,
所以（-&，3/2）是单调递减，（3/2,+&）是单调递增尘薯皮
。。。。我是姐姐，不是大哥手正
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向量x=（(t-3+2*根号3)/2，-1+(t-3)*(根号3)/2)
向量y=(t/2-根号3*k,k+根态首扒号3*t/2)
k=(t*t-3*t)/4,在帆昌 t<3/2递减，t>3/芹兄2递增
x和y相乘再利用数量积可得出k的函数再求单调性