I am not completely sure about using to get to the surd value for and , however I do know another way:
You can try represent and with angles that we now the surd form:
By using a double angle formula, you can now find the exact value of and .
Show that and deduce a similar expression for
Hence find the surd form of the values of and
i have completed the first two parts, for the second i got the equality
now i only have the last part to do and i'm lost.