y=ln cos(2x+1)
y'=[ln cos(2x+1)]'
=1/cos(2x+1)*[cos(2x+1)]'
=1/cos(2x+1)*[-sin(2x+1)]*(2x+1)'
=-2/cos(2x+1)*sin(2x+1)
=-2tan(2x+1)
y=ln cos(2x+1)
y'=[ln cos(2x+1)]'
=1/cos(2x+1)*[cos(2x+1)]'
=1/cos(2x+1)*[-sin(2x+1)]*(2x+1)'
=-2/cos(2x+1)*sin(2x+1)
=-2tan(2x+1)