I believe compulsory or not depends on the school
I was very weak in maths since secondary 2.
Because of this i was not allowed to take A maths. The reason given
was that it will be too hard for us(everyone who failed E sec 2
maths) to cope.
Eventually i took engineering maths and Higher Engineering maths
in poly. It wasn't so hard after all. Engineering maths is very
similar to A maths.
If you decide to drop A maths, make sure your E maths is good.
Be very familiar with complicated fractions with algebra, how to
make subject of the formula, trigo, factorising, expanding,
simplifying equationsetc.
If you plan to study engineering, please take A maths. Because
there are lots of equations used to represent behaviours of circuit
diagrams, and most of which would need some basic understanding of
A maths.
Engineering maths covers things like: Differentiation/Integration,
indices, the waveforms(y=mx+c, sin/cos, pi, etc), statistics,
probability, complex numbers, matrices(i think e maths cover some
basics), taylor series, fourier series.