I don't know if anyone has actually answered the poor guy's question yet, including me! Peter, you do NOT have to memorise any formulae EXCEPT for simple formulae:
Pythagoras's Theorem: c^2 = a^2 + b^2
AREA OF PLANE SHAPES:
Square: A^2
Rectangle = LB
Triangle: 1/2 x bh
The formulae for special plane shapes should be included on the FORMULAE SHEET. You should know how to calculate the area of trapeziums, rhobmuses/kites and parallelograms anyway. Have a look at an HSC General Mathematics past paper - it contains all the formulae on the School Certificate Mathematics test Formulae Sheet. But don't worry, the General Maths formulae sheet also contains a few extra formulae.
REMEMBER
You do NOT have to memorise many formulae. You also do not have to know how "simple" formulae are derived. For example, they are never going to ask in a Year 10 test, "Show how the formula for the surface area of a sphere, SA = 4 x pi x r^2 is derived". That's an HSC Mathematics Extension 2 question, of course.