An angle of 60 degrees with the negative y-axis could mean 60 degrees clockwise or counterclockwise, which translates to two possible angles (starting from the positive x-axis and moving counterclockwise) of 210 degrees or 330 degrees.
Then the horizontal component [tex]v_x[/tex] of a velocity vector [tex]\mathbf v[/tex] with magnitude [tex]5.00\,\dfrac{\mathrm m}{\mathrm s}[/tex] could be one of two expressions:
[tex]v_x=\left(5.00\,\dfrac{\mathrm m}{\mathrm s}\right)\cos210^\circ=-4.33\,\dfrac{\mathrm m}{\mathrm s}[/tex]
[tex]v_x=\left(5.00\,\dfrac{\mathrm m}{\mathrm s}\right)\cos330^\circ=4.33\,\dfrac{\mathrm m}{\mathrm s}[/tex]
