Calculate (7-i*sqrt(6))*(13+i*sqrt(6))

We expand the parentheses to get to the equation: 713-13isqrt(6)+7isqrt(6)-iisqrt(36) which after some further calculations equals to: 91-6isqrt(6)+sqrt(36) [We got +sqrt of 36 because ii*=sqrt(-1)sqrt(-1)= -1, which results in -1(-sqrt(36))=sqrt(36)].Realizing that sqrt(36)=6 we get to the final result: 97-6isqrt(6)