Q7
for 7 ii, u need to set up an inequality of the sum of savings
using B and A. Should be a pretty simple and straightforward
solution.
Q9
For Q9, the problem with your workings is because of usage of
formulas without understanding the potential consequences. Took me
a while to understand because your workings did not define D, and
for vectors, by convention, it is actually small d. Your school
teachers may not have problems with your answers, but I think this
will give problems to Cambridge examiners who will be marking your
papers in A level. So take note on that.
The consequence in this scenario is that modulus introduce
additional answers, and it's because the second plane could be
either on the other side of A or the same as plane 1, but still 3
times the distance.
One solution is to find the foot of perpendicular from A to
plane 1. Then use ratio theorem to find a point on plane 2, so that
you can get the correct direction. Since they are parallel, you
already have the normal vector, and you can find the value of D
without the implications of a modulus.
Q10
For iii. Typically, for such questions, there will be two
solutions. One refers to the original point where you calculated
the normal from. This answer don't need reject, but it isn't the
answer we are looking for.
The other value will be the answer we are looking for.
For iv.
θ = tan inverse
(y/x)
so
dθ/dt = difference [tan
inverse (y/x)] implicitly w.r.t. t
Think you can try liao.