No, Ikleyn, this student wrote me this in his "thank-you" letter.
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It said to factor it. Sorry!
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This student apparently is studying very complicated algebraic factoring
methods.
The quartic is factorable algebraically using radicals (square roots):
We try to reduce it to a quadratic in y², by substituting a linear form for x,
say x=ay+b
We see if we can choose "a" and "b" so that the terms in y³ and y become 0.
It isn't difficult to see that the only two terms in y³ are
4a³by³ - 8a³y³ = 4a(b-2)y³, which would be 0 for all y if b=2
There are four terms in y, and they are
4ab^3y - 24 ab^2y + 44aby - 24ay
Substituting b=2
32ay - 96ay + 88ay - 24ay which, luckily, equals 0
Therefore, we can simply take a = 1, and b = 2
Then x = ay+b = y+2
becomes
which simplifies to
and by the quadratic formula,
So there are two real zeros for y
,
And there are two imaginary zeros for y
,
Since √2 is greater than 1,
,
So the factorization in terms of y is:
Since x = y+2, we substitute x-2 for y
Edwin