# Complex Numbers...Find x

• December 28th 2008, 01:17 PM
magentarita
Complex Numbers...Find x
Solve for x: (3 + 2i) + (4 + xi)= 7 - 5i

(1) -7
(2) -3
(3) 3
(4) 7
• December 28th 2008, 01:33 PM
Jhevon
Quote:

Originally Posted by magentarita
Solve for x: (3 + 2i) + (4 + xi)= 7 - 5i

(1) -7
(2) -3
(3) 3
(4) 7

3 + 2i + 4 + xi = 7 + (2 + x)i

now equate real and imaginary parts...
• December 28th 2008, 08:17 PM
Rapha
Hi magentarita.

Its simple math:

$(3 + 2i) + (4 + xi)= 7 - 5i$

// - 3 // -2i

$4+x*i = 4 -7i$

//-4

$x*i = -7i$

// : i

=> $x = -7\frac{i}{i} = -7$

Kind regards,
Rapha
• December 29th 2008, 09:09 PM
magentarita
what does......
Quote:

Originally Posted by Rapha
Hi magentarita.

Its simple math:

$(3 + 2i) + (4 + xi)= 7 - 5i$

// - 3 // -2i

$4+x*i = 4 -7i$

//-4

$x*i = -7i$

// : i

=> $x = -7\frac{i}{i} = -7$

Kind regards,
Rapha

In this case, what does the symbol // mean?
• December 29th 2008, 09:15 PM
magentarita
ok....
Quote:

Originally Posted by Jhevon
3 + 2i + 4 + xi = 7 + (2 + x)i

now equate real and imaginary parts...

7 + (2 + x)i = 7 - 5i

7 + 2i + xi = 7 - 5i

7 - 7 + xi = -2i - 5i

xi = -7i

x = -7i/i

x = -7

Is this correct?
• December 29th 2008, 09:27 PM
Prove It
Quote:

Originally Posted by magentarita
7 + (2 + x)i = 7 - 5i

7 + 2i + xi = 7 - 5i

7 - 7 + xi = -2i - 5i

xi = -7i

x = -7i/i

x = -7

Is this correct?

Yes, but it's easier to just say

Real parts: $7 = 7$, correct.

Imaginary parts: $2 + x = -5 \implies x = -7$.
• December 29th 2008, 09:48 PM
Rapha
Quote:

Originally Posted by magentarita
In this case, what does the symbol // mean?

It means nothing.
I just use(d) it to show the steps.
Don't you know some Programming languages (like Java)? Sometimes you use " // " to comment several lines out.

Regards,
Rapha
• December 29th 2008, 10:02 PM
magentarita
Thanks