Question 1045313
2 sqrt (3)+4 sqrt(5)
conjugate is 
2 sqrt(3)-4 sqrt(5)
Product is
4*3-8 sqrt (15)+8 sqrt (12)-80=-68-8 sqrt(15)+16 sqrt (3)
The first term squares 2 sqrt(3), which is 4*3
The internal products are written, and 8 sqrt(12)=16 sqrt (3), because sqrt (12)=2 sqrt(3)
The last product is minus 16*5
The conjugate is the same binomials subtracted (or added), so that the first and last radical terms are eliminated.