|5-6i|

[JordanRRR]

The problem is 5-6i in absolute value - | 5-6i |.

All I know is that the answer is radical 29(edit) but have no idea how to get it. Any help is greatly appreciated.

 

[tkhunny]

29? No, I don't think so.

sqrt(5^2 + (-6)^2) = sqrt(25+36) = sqrt(61)

 

[JordanRRR]

The choices are:

A) 5+2i B)Radical 21 C)Radical 7 D)Radical 29

 

[tkhunny]

E sqrt(61)

Maybe B is a typo?

 

[JordanRRR]

I found out that you just take 5-6i and multiply by its conjugate (5+6i) and you do end up with 29.

 

[stapel]

I found out that you just take 5-6i and multiply by its conjugate (5+6i) and you do end up with 29.

I'm not sure I see how that's possible.

. . .(5 - 6i)(5 + 6i)

. . . . .= (5)(5) + (5)(6i) + (-6i)(5) + (-6i)(6i)

. . . . .= 25 + 30i - 30i + 36i²

. . . . .= 25 - 36

. . . . .= -9

In any case, the modulus of a complex number, |a + bi|, is, as was pointed out earlier, the square root of the sums of the squares of a and b. So the modulus (what was original posted) is:

. . .|5 - 6i|

. . . . .= sqrt[5² + (-6)²]

. . . . .= sqrt[25 + 36]

. . . . .= sqrt[61]

Eliz.

Mathwords: Absolute Value of a Complex Number
MathWorld: Complex Modulus

 

[tkhunny]

I found out that you just take 5-6i and multiply by its conjugate (5+6i) and you do end up with 29.

...and this causes one to wonder if we have the right problem statement. Did you report it EXACTLY as it appeared on your exam or assignment?