svpp c'est pour demain

EX 2
(√7+√2)(√7-√2)
= √7²-7√2+7√2-√2²
= 7-2
= 5

(2√3-3)(2√3+3)
= 4√3²+6√3-6√3-9
= 4x3-9
= 12-9
= 3

Ex 3
A = √80-√20(2-√15)
A = 4√5-2x2√5+2√(5x15)
A = 4√5-4√5+2x5√3
A = 10√3

B = √6(√3+5)-√150
B = √(6x3)+5√6-5√6
B = √(3x3x2)
B = 3√2