JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Self Evaluation Test - Complex Numbers and Quadratic Equations

  • question_answer
    The greatest and the least absolute value of \[z+1,\] where \[|z+4|\le 3\] are respectively

    A) 6 and 0            

    B) 10 and 6         

    C) 4 and 3            

    D) None of these

    Correct Answer: A

    Solution :

    We have \[|z+1|=|z+4-3|\]        ...(i) Now  \[|z+4-3|\le |z+4|+|-3|\le 3+3=6\] [Given \[|z+4|\le 3\] & \[|-3|=3\]] \[\therefore \,\,|z+1|\le 6\] Again \[|z+1|\,\,\ge \,\,0\] [modulus is always non- negative] \[\therefore \] Least value of \[|z+1|\] maybe zero, which occurs when \[z=-1,\]For \[z=-1,\]\[|z+4|=|-1+4|=3\] Which satisfies the given condition that \[|z+4|\,\,\ge \,\,3\] Hence, the least and the greatest values of \[|z+1|\] are 0 and 6


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