Ya lor, we always have this problem ie if we give an
intermediate value for the answer for part (a) correct to 3 sig fig
and this intermediate is required for the calculation for the
answer for part (b), should we substitute the corrected
intermediate value or the exact intermediate value in the
calculation for the answer for part (b) huh ?
U can use the exact intermediate value for part b if its not
difficult to fish out from the calculator's
memory....otherwise...using 4 s.f(or above if U are really
kiasu)will do...if ur final answer is to be in 3 s.f...
Remember its not the extra digits U put in that shows ur
understanding.
Simple example:
calculate cos (pi/12) x 20.
Using exact value :
cos (pi/12) x 20
=cos (0.26179938779) x 20
=19.3 radians (3 s.f)
Using 4 s.f in intermediate value :
cos (pi/12) * 20
= cos (0.2618) * 20
=19.3 radians (3 s.f)
end of the day the final answer will not vary by a lot....what
the examiners want to know if whether U know ur s.f....not how many
digits U can squeeze into the width of an A4-sized exam
paper.
