![\sqrt{ \frac{-49}{(7-2i)-(4+9i) } } ](https://tex.z-dn.net/?f=%20%20%5Csqrt%7B%20%5Cfrac%7B-49%7D%7B%287-2i%29-%284%2B9i%29%20%7D%20%7D%20%0A)
This one is quite the deal, but we can begin by distributing the negative on the denominator and getting rid of the parenthesis:
![\frac{ \sqrt{-49}}{7-2i-4-9i}](https://tex.z-dn.net/?f=%20%5Cfrac%7B%20%5Csqrt%7B-49%7D%7D%7B7-2i-4-9i%7D%20)
See how the denominator now is more a simplification of like terms, with this I mean that you operate the numbers with an "i" together and the ones that do not have an "i" together as well. Namely, the 7 and the -4, the -2i with the -9i.
Therefore having the result:
![\frac{ \sqrt{-49} }{3-11i}](https://tex.z-dn.net/?f=%20%5Cfrac%7B%20%5Csqrt%7B-49%7D%20%7D%7B3-11i%7D%20)
Now, the
![\sqrt{-49}](https://tex.z-dn.net/?f=%20%5Csqrt%7B-49%7D%20)
must be respresented as an imaginary number, and using the multiplication of radicals, we can simplify it to
![\sqrt{49} \sqrt{-1}](https://tex.z-dn.net/?f=%20%5Csqrt%7B49%7D%20%20%5Csqrt%7B-1%7D%20)
This means that we get the result 7i for the numerator.
![\frac{7i}{3-11i}](https://tex.z-dn.net/?f=%20%5Cfrac%7B7i%7D%7B3-11i%7D%20)
In order to rationalize this fraction even further, we have to remember an identity from the previous algebra classes, namely:
![x^2 - y^2 =(x+y)(x-y)](https://tex.z-dn.net/?f=x%5E2%20-%20y%5E2%20%3D%28x%2By%29%28x-y%29)
The difference of squares allows us to remove the imaginary part of this fraction, leaving us with a real number, hopefully, on the denominator.
![\frac{7i (3+11i)}{(3-11i)(3+11i)}](https://tex.z-dn.net/?f=%20%5Cfrac%7B7i%20%283%2B11i%29%7D%7B%283-11i%29%283%2B11i%29%7D%20)
See, all I did there was multiply both numerator and denominator with (3+11i) so I could complete the difference of squares.
See how
![(3-11i)(3+11i)= 3^2 -(11i)^2](https://tex.z-dn.net/?f=%283-11i%29%283%2B11i%29%3D%203%5E2%20-%2811i%29%5E2%20)
therefore, we can finally write:
![\frac{7i(3+11i)}{3^2 - (11i)^2 }](https://tex.z-dn.net/?f=%20%5Cfrac%7B7i%283%2B11i%29%7D%7B3%5E2%20-%20%2811i%29%5E2%20%7D%20)
I'll let you take it from here, all you have to do is simplify it further.
The simplification is quite straightforward, the numerator distributed the 7i. Namely the product
![7i(3+11i) = 21i+77i^2](https://tex.z-dn.net/?f=7i%283%2B11i%29%20%3D%2021i%2B77i%5E2%20)
.
You should know from your classes that i^2 = -1, thefore the numerator simplifies to
![-77+21i](https://tex.z-dn.net/?f=-77%2B21i)
You can do it as a curious thing, but simplifying yields the result: