100nē + 400n - 32,000 = 0
Factorise 100
100(nē + 4n - 320) = 0
Write down all the ways to factorise 320, starting
with 320·1 and since the last sign is - write the
difference of the two factors to the side:
320·1 320-1 = 319
160·2 160-2 = 158
80·4 80-4 = 76
64·5 64-5 = 59
40·8 40-8 = 32
32·10 32-10 = 22
20·16 20-16 = 4
We find the coefficient of the middle term, which is 4,
in the list of differences, so we use 20 and 16:
100(n + 20)(n - 16) = 0
To solve that we use the zero-factor principle:
100 = 0; n + 20 = 0; n - 16 = 0
n = -20; n = 16
Edwin