Question

Identify a necessary and sufficient condition for two complex numbers a, b to have a real sum and a real product

Answers

  1. Either both numbers are conjugated or both numbers are real numbers.

    What are complex numbers?

    • Complex numbers are made up of two parts: a real number and an imaginary number.
    • Complex numbers serve as the foundation for more complex math, such as algebra.
    Consider two complex numbers q and p such that,q=c+id and p=a+ib.
    • A.T.Q. PQ is real and p + q real.
    • pq=(ac−bd)+(bc+ad)i
    Since PQ is real, the imaginary part must be zero, hence bc+ad=0 or:
    • bc=−ad
    Then,
    • p+q=(a+c)+(b+d)i
    Here also b+d must be zero or:
    • d=−b
    So putting d=−b in bc=−ad, we will get,
    • b(c−a)=0
    So either,
    • b=d=0
    • or, a=c,b=−d
    So either p and q are conjugated
    • p=a+bi,q=a−bi
    or both are real
    • p=a,q=c
    Therefore, either both numbers are conjugated or both numbers are real numbers.
    Know more about complex numbers here:
    #SPJ4
    The correct question is given below:
    If the product and the sum of two complex numbers are real, what can we say about the numbers? Prove it.

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