ab3 = 40
a = 5, b = +/-2
differentiating implicitly: a'b3 + 3b2b'.a = 0
rearrange for a': da/dt = -[3b2.db/dt.a]/b3 = -7.5, after substituting for given values.
Re: Is it really so bad to study from study guides?
Studying from study guides was pretty much all i did for the sciences, and i ended up with 99.05.
but hey whatever works for you
It's not really necessary for anyone to stop exercising because they're doing their HSC. I've been exercising regularly throughout the HSC and I've found that it's been really beneficial.