1.应用拉格朗日乘数法,求下列函数的条件极值:-|||-(1) (x,y)=(x)^2+(y)^2, 若 +y-1=0;-|||-(2) (x,y,z,t)=x+y+z+t, 若 =(c)^4 (其中 ,y,z,tgt 0,cgt 0);-|||-(3) (x,y,z)=xyz, 若 ^2+(y)^2+(z)^2=1 +y+z=0.