Solve Solve x^3+18x^2+108x-108=0
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1 Answer

Substitute y+a for x:

y³+3ay²+ 3a²y+    a³+

      18y²+36ay+ 18a²+

                108y+108a-108=0,

y³+(3a+18)y²+(3a²+36a+108)y+a³+18a²+108a-108=0.

If 3a+18=0, a=-6 and the y² term cancels out.

But so does the y term!

What remains is:

y³-324=0, y³=324, y=6.8682...

Therefore x=∛324-6=0.868285455 approx.

by Top Rated User (711k points)

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