Polar Coordinates

Hi, we did some simple excersizes with rectangular and polar coordinates and are now tasked with using matlab to do the calculations for us. This is my senior year in engineering and I haven't really used much Matlab since my freshmen year so it's a bit of a struggle. I have managed to get all of the other problem s in Matlab but am stuck with this last one. Any help would be greatly appreciated. Thanks in advance:

Perform the operation using polar coordinates, and express the result in standard rectangular form: (2+j)^2

I used the following function to convert 2+j to polar coordinates:

>> [Theta_a, R_a] = cart2pol( real(2), imag(j) )

Theta_a =

0.4636


R_a =

2.2361

So I now have the function is polar coordinates but I do not know how to square this function before converting ot back to rectangular coordinates uning this function:

[x, y] = pol2cart(Theta_a, R_a);
new_a = x + y*i

The answer should be: 5[cos(2theta) + j sin(2theta)], theta=tan^-1 (1/2)

Can anyone tell me what I need to do to square that function?

Thanks