y=(5x-1)/(4x+1)值域,

y=(5x-1)/(4x+1)值域,
y=(5x-1)/(4x+1)值域,

y=(5x-1)/(4x+1)值域,
y=(5x-1)/(4x+1)
=(5x+5/4-9/4)/(4x+1)
=(5x+5/4)/(4x+1)-(9/4)/(4x+1)
=5/4 -(9/4)/(4x+1)
∵ 4x+1≠0
∴ -(9/4)/(4x+1)≠0
∴ y≠5/4
即值域为{y|y≠4/5}

y=20x^2+x-1;x=-2/(20*2)=-0.05时，y最小y=20*0.05^2-0.05-1=-1;所以y>=-1

y=(5x-1)/(4x+1)
=(5x+5/4-9/4)/(4x+1)
=(5x+5/4)/(4x+1)-9/4(4x+1)
=5/4 -9/4(4x+1)
∵ 4x+1≠0
∴ -9/4(4x+1)≠0
∴ y≠5/4
即值域:{y|y≠5/4}