9.对于变量x和变量y,通过随机抽样获得10个样本数据 ((x)_(i),(y)_(i))(i=1,2,3... ,10), 变量x和变-|||-量y具有较强的线性相关并利用最小二乘法获得回归方程为 hat (y)=-2x+a, 且样本中心点为-|||-(6,9.3),则下列说法正确的是-|||-A.变量x和变量y呈正相关 B.变量x和变量y的相关系数 lt 0-|||-C. a=21.3 D.样本数据(5,12 )比(7,5)的残差绝对值大-|||-10.已知等差数列({an)的首项为a1,公差为d,前n项和为Sn,若 _(20)lt (S)_(18)lt (S)_(19), 则下列说法正确-|||-的是-|||-A. _(1)gt 0 B. gt 0-|||-C. |(a)_(18)+(a)_(19)|gt |(a)_(20)+(a)_(21)| D.数列 dfrac {{S)_(n)}({a)_(n)}} 的所有项中最小项为 dfrac ({S)_(20)}({a)_(20)}-|||-11.已知直四棱柱中 -(A)_(1)(B)_(1)(C)_(1)(D)_(1), 底面AB CD为菱形且 angle BAD=(60)^circ , 四边形AA1C1C是边-|||-长为 sqrt (6) 的正方形,点P为底面ABCD内一动点(不包含边界),满足 _(1)Pykparallel 平面A1C1D,则-|||-下列说法正确的是-|||-A.异面直线AB与C,D所成角为60° B.任意点P均满足 _(1)Pbot (A)_(1)(C)_(1)-|||-C.点P的轨迹长度为 dfrac (sqrt {6)}(2) D.三棱锥 -(A)_(1)(C)_(1)(D)_(1) 的外接球表面积为14π-|||-12.已知函数 (x)=(x)^2(e)^x+4+dfrac (1)({e)^x}+mx 有四个不同零点,分别为x1,x2,x3, _(4)((x)_(1)lt (x)_(2)lt (x)_(3)lt (x)_(4)), 则-|||-下列说法正确的是-|||-A. -1lt (x)_(3)lt 0 B. ^(x_{1)+(x)_(4)+4}=dfrac (1)({x)_(1)(x)_(4)}-|||-C. _(2)(e)^(x_{2)}=(x)_(3)(e)^(x_{3)}, D. ln ((x)_(1)(x)_(2)(x)_(3)(x)_(4))+(x)_(1)+(x)_(2)+(x)_(3)+(x)_(4)=-8