18. a) (5√3 + √5)² - 5√5 × √12 =
= 75 + 10√15 + 5 - 5√5 × 2√3 =
= 75 + 10√15 + 5 - 10√15 = 80
b) ( √6 - √3)² + (2√2 - 3)(2√2+3) =
= 6 + 2√18 + 3 + 4 × 2 - 9 =
= 6 - 6√2 + 3 + 8 - 9 = 8 - 6√2
19. a) ( √5 + 1 )² - √5 × ( 2√5 + 2 ) =
= 5 + 2√5 + 1 - 10 - 2√5 = -4
b) ( 2√7 - 3)² + 2√7 × ( 6 - √7 ) =
= 28 - 12√7 + 9 + 12√7 - 14 = 23
20. a) (4√2-√30)(4√2+√30)-3(√5+1)² =
= 16 * 2 - 30 - 3(5+2√5 + 1)=
= 32 - 30 - 3(6+2√5) =
= 32-30-18-6√5 = - 16 - 6√5
b) 4(√3+1)²-√3(8-√3)-(√21-√2)(√21+√2) =
= 4(4+2√3)-8√3+3-19=
=16+8√3-8√3+3-19 = 0
