Confused about complex numbers

[snate]

Can someone please explain what's going on at 47:40
Thanks in advance.

 

[mfb]

$|a+b|^2 = (a+b)(a+b)^* = aa^* + bb^* + a^*b + ab^*= |a|^2 + |b|^2 + a^*b+ ab^*$ where * is the complex conjugation.

 

[snate]

$|a+b|^2 = (a+b)(a+b)^* = aa^* + bb^* + a^*b + ab^*= |a|^2 + |b|^2 + a^*b+ ab^*$ where * is the complex conjugation.

Thanks you!