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LetP(r1)=anr1n+an−1r1n−1+...+a1r1+a0 be a polynomialwith real coefficientsan,....,a0 . Prove that if r1 is azero ofP(r) , then so is its complex conjugate r1. [Hint:Show thatP(r)¯=P(r¯) , where the bar denotes complexconjugation.]

Short Answer

Expert verified

If r1 is a zero of the given polynomial P(r) then so is its complex conjugate r1.

Step by step solution

01

Step 1: Complex Conjugation

A complex conjugate of a complex number is another complex number that has the same real part as the original complex number and the imaginary part has the same magnitude but opposite sign. The product of a complex number and its complex conjugate is a real number.

02

Use of Complex Conjugation properties

Suppose complex number r1 is a zero of the given polynomial P(r). Hence P(r1)=0:

P(r1)=0⇒P(r1)¯=0¯=0

Using properties of complex conjugation:

P(r1)¯=(anr1n+an−1r1n−1+...+a1r1+a0)¯=anr1n¯+an−1r1n−1¯+...+a1r1¯+a0=P(r1¯)=0

Hence, the final answer is:

Ifr1 is a zero of the given polynomial P(r) then so is its complex conjugate r1.

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