Simple three-phase circuit question
You do not need frequency. When the frequency and time are plugged into the instantaneous equations, the sine waves can be sketched.  

Angular velocity: \$2πf = 2π 50Hz = 314 rad/s\$

$$u_A = 100\ cos(314t)\ V$$

This means \$θ_A = 0\$, so \$ θ_B = θ_A\ -\ 2π/3\$ and \$ θ_C = θ_A\ +\ 2π/3\$.  So the instantaneous equations for the other two phases are:
$$u_B = 100\ cos(314t \ -\ 2π/3)\ V$$
$$u_C = 100\ cos(314t \ +\ 2π/3)\ V$$

with phase voltages as vectors, \$U_A = 100/\sqrt{2}\ \measuredangle 0\ V \$, \$U_B = 100/\sqrt{2}\ \measuredangle -2π/3\ V \$ and \$U_C = 100/\sqrt{2}\ \measuredangle \ 2π/3\ V \$. 

In a wye, \$ V_{Line} = \sqrt {3} V_{Phase}\$ and lead phase voltages by 30°.

$$ U_{AB} = U_A - U_B = \sqrt {3}\ 100/\sqrt{2} \ \measuredangle π/6\ V$$ 
$$ U_{BC} = \sqrt {3}\ 100/\sqrt{2} \ \measuredangle -π/2\ V$$ 
$$ U_{CA} = \sqrt {3}\ 100/\sqrt{2} \ \measuredangle 5π/6\ V$$ 

So enter the vectors as complex numbers (\$U_C=100/\sqrt{2}\ e^{j\ 2π/3}\$) into a TI-83 or work out sin and cos components to get real and imagenary components.