1.设x=3sina,代入得y=√[9-(3sina)^2]+3sina+4. =3[cosa]+3sina+4=3√2sin(a+θ）+4由于-1<=sin(a+θ)<=1所以 4-3√2<=y<=4+3√22.y=√(x+1)-√(x-1).= [(x+1)-(x-1)]/[√(x+1)+√(x-1)] =2/{√(x+1)+√(x-1)]因为x在[1，+无穷）内y是 展开
1.设x=3sina,代入得y=√[9-(3sina)^2]+3sina+4. =3[cosa]+3sina+4=3√2sin(a+θ）+4由于-1<=sin(a+θ)<=1所以 4-3√2<=y<=4+3√22.y=√(x+1)-√(x-1).= [(x+1)-(x-1)]/[√(x+1)+√(x-1)] =2/{√(x+1)+√(x-1)]因为x在[1，+无穷）内y是减函数所以 0<y<=√2 收起
