求值域!y=4x+1/x-1(x>1)求值域!y=4x+1/(x-1)(x>1)

求值域!y=4x+1/x-1(x>1)求值域!y=4x+1/(x-1)(x>1)
求值域!y=4x+1/x-1(x>1)
求值域!y=4x+1/(x-1)(x>1)

求值域!y=4x+1/x-1(x>1)求值域!y=4x+1/(x-1)(x>1)
令t=x-1,t>0.x=t+1
y=4x+1/(x-1)
=4(t+1)+1/t
=4t+4+1/t
=(2√t-1/√t)^2+8
∵(2√t-1/√t)^2≥0
∴y≥8
值域是[8,+∞).