# Complex Equation Help!

• November 23rd 2009, 04:01 PM
wafflemypanda
Complex Equation Help!
So, I'm having trouble with these complex equations. Any help would be great!

(2+3i)(3-4i)

2+i/3i

1+2i/1-i

Thanks again.
• November 23rd 2009, 04:13 PM
qmech
Lets try something like your problems

(3+4i)(1+2i)
= 3*1 + 4i*1 + 3*2i + 4i*2i
= 3 + 4i + 6i + 8i^2
= 3 - 8 + 10i
= -5 + 10i.

See how it's done?

(3+4i) / ( 2+i )
= (3+4i)(2-i) / (2+i)(2-i) multiply by 1, where 1 = (2-i)/(2-i).
= multiply out the top / multiply out the bottom.
• November 23rd 2009, 07:33 PM
Stroodle
Remember that $i^2=-1$ and if you multiply a complex number by its conjugate you will get a real number.

e.g. the conjugate of $a+bi$ is $a-bi$