2. (a) Find the real root of the equation z3 + z + 10 = 0 given that one root is 1 − 2i.
Show that z = i is a root of the equation z4 + z3 + z − 1 = 0. Find the three
other roots.
1
Expert's answer
2020-05-26T18:13:19-0400
z=1+2i is also a root of equation. We obtain this by conjugating the equation. Dividing the polynomial z3+z+10 by (z−1−2i)(z−1+2i)=z2−2z+5
we receive z+2 . Thus, z=−2 is the real root.
Now we consider equation z4+z3+z−1=0 . We will check that z1=i is a root of equation. Namely, we have: z14+z13+z1−1=1−i+i−1=0
It is clear that z2=−i is also a root of equation.
This can be obtained from the fact that z2=zˉ1
We shall divide the equation by (z−i)(z+i)=z2+1 .
Then one receives z2−1+z. It remains to solve z2+z−1=0 .
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