(2√3+5)(√3-√5)
Just using normal "FOIL"....we have...
2√3 *√3 = 2*3 = 6
2√3 *(-√5) = -2√15
5 * √3 = 5√3
5 * (-√5) = -5√5
And combining terms, we have
6- 2√15 + 5√3- 5√5