Accedmychevron_right11thchevron_rightmathchevron_rightComplex Numberschevron_rightExercise 1.3

Question 5

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Solve the following equations .

(iv) z35z2+z5=0z^3 - 5z^2 + z - 5 = 0

Solution

Group terms:(z35z2)+(z5)=z2(z5)+1(z5)Factor out (z5):=(z5)(z2+1)=0Apply zero product property:z5=0    z=5z2+1=0    z2=1    z=±iTherefore: z=5,i,i\begin{aligned} & \boxed{\text{Group terms:}} \\ \\ & (z^3 - 5z^2) + (z - 5) = z^2(z - 5) + 1(z - 5) \\ \\ & \boxed{\text{Factor out } (z - 5):} \\ \\ & = (z - 5)(z^2 + 1) = 0 \\ \\ & \boxed{\text{Apply zero product property:}} \\ \\ & z - 5 = 0 \implies z = 5 \\ \\ & z^2 + 1 = 0 \implies z^2 = -1 \implies z = \pm i \\ \\ & \boxed{\text{Therefore: } z = 5, i, -i} \end{aligned}