已知空间三点A(0,1,2)B(1,2,2)C(-1,1,4),设m=→AB,n=→AC (答:(1)│m│=√[(1-0)^2+(2-1)^2+(2-2)^2]=√2 │n│=√[(-1-0)^2+(1-1)^2+(4-2)^2]=√5 (2)m=→AB=(1,1,0)n=→AC =(-1,0,2)tm+n=(t-1,t,2)tm-2n=(t+2,t,-4)因为所成角为钝角,所以 (t-1)*(t+2)+(t)*(t)+(2)*(-4)<0 ...
如图已知抛物线C:y^2=2px和圆M:(x-4)^2+y^2=1,过抛物线上一点H(x...答:(I)M(4,0)到抛物线y^=2px的准线的距离为17/4,∴准线为x=-1/4,p=1/2,抛物线C的方程为y^=x.① (II)∠AHB的平分线HM⊥x轴时H为(4,土2),H为(4,2)时,设HA(HB)的方程为y-2=k(x-4),即kx-y+2-4k=0,M到HA的距离=2/√(k^+1)=1,∴k^=3,k=土√3,把y=√3x...