Complex Number

Algebra Level 4

Determine the number of solutions of the equation, where z z is a complex number.

z 2 + z = 0 \large z^2 + |z| = 0

2 3 1 0

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2 solutions

Tom Engelsman
Aug 16, 2016

Let z = a + b i z = a + bi be any complex number. The above equation yields:

( a + b i ) 2 + a 2 + b 2 = 0 ; (a+bi)^2 + \sqrt{a^2 + b^2} = 0;

or a 2 b 2 + 2 a b i + a 2 + b 2 = 0 a^2 - b^2 + 2abi + \sqrt{a^2 + b^2} = 0

which requires both the real and the imaginary parts to equal zero:

a 2 b 2 + a 2 + b 2 = 0 ; 2 a b = 0 a^2 - b^2 + \sqrt{a^2 + b^2} = 0; 2ab = 0 .

The imaginary part is zero iff a a or b = 0 b = 0 . Hence for the real part:

If a = 0 a = 0 , then we have b 2 + b = 0 b = ± b 2 . -b^2 + |b| = 0 \Rightarrow b = \pm b^2. Taking b = b 2 b = b^2 yields b = 0 , 1 b = 0, 1 and b = b 2 b = -b^2 yields b = 0 , 1 b = 0, -1 , which in turn produce the ordered-pairs ( a , b ) = ( 0 , 0 ) ; ( 0 , 1 ) ; ( 0 , 1 ) (a,b) = (0,0); (0,-1); (0,1) .

If b = 0 b = 0 , then we have a = a 2 a = 0 |a| = -a^2 \Rightarrow a = 0 and ( a , b ) = ( 0 , 0 ) (a,b) = (0,0) is the only ordered-pair solution under this condition.

Thus, ( a , b ) = ( 0 , 0 ) ; ( 0 , 1 ) ; ( 0 , 1 ) (a,b) = (0,0); (0,-1); (0,1) (or z = 0 , ± i \boxed{z = 0, \pm i} ) are the only solutions

The value of i , i, and i -i are undefined, and they are undefinable.

. . - 3 months, 2 weeks ago

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That is irrelevant as we're looking to find complex numbers z that satisfy the above equation.

tom engelsman - 3 months, 2 weeks ago
Aryan Mehra
Apr 30, 2017

Use basics and always stick to the original form of the complex numbers x +yi. Thus get a quadratic or quartic equation where we face a compulsion to put x or y as 0. Hence using simpke lohic the answer comes out to be 0 i and -i. There are thus three solutions.

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