Factors of 42 won't add up to 15. What you're looking for is two sets of numbers independent of each other.
The first set must multiply to make 15 (as in a and c in my example below).
The second set must multiply to make 42 (as in b and d below). This is what you're used to doing by the looks of things
Since a trinomial can be written as we expand this to give .
Factors of 42: 1, 2, 6, 7 , 21, 42
Factors of 15: 1, 3, 5, 15
It's very unlikely to be any of the extrema so pick the middle pairs first.
For your sum you need to find when it is known that and
Hi JayRich88,
as e^(i*pi) showed,
you are looking for 4 values a, b, c and d.
But there are only 3 terms in the equation, so we don't have enough clues to solve
using a few simultaneous equations.
Hence it's necessary to examine how they combine.
You need to factorise -42 and 15 and combine these two sets of factors
within parentheses as already shown to achieve -17x.
This is because -42 and 15 themselves do not combine to give -17x.
Usually these will be the most obvious ones, like 5 and 3, 6 and 7.
and in this case they are!
It doesn't always happen to be the most expected ones,
but that's normally the best place to start.