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  • Tell me? - Complex numbers and quadratic equations - JEE Main-10

Let z= \left ( 2a-3 \right )+i\left ( 4a+5 \right ) is a complex number which is purely imaginary, then 9m\left ( z \right ) equals \left ( a\: \epsilon \: R \right )

  • Option 1)

    9

  • Option 2)

    10

  • Option 3)

    11

  • Option 4)

    12

 

Answers (1)

best_answer

Since z is purely imaginary so Re(z)=0

\Rightarrow 2a-3=0  \Rightarrow a=\frac{3}{2}

\therefore Im (z) = 4a+5 = 4\left ( \frac{3}{2} \right )+5=11

\therefore Option (C)

 

Purely Imaginary Complex Number -

z=x+iy, \boldsymbol{x=0}, y\epsilon R

& i2=-1

- wherein

Real part of z = Re (z) = x & Imaginary part of z = Im (z) = y

 

 

 


Option 1)

9

This is incorrect

Option 2)

10

This is incorrect

Option 3)

11

This is correct

Option 4)

12

This is incorrect

Posted by

Plabita

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