a) (√ 7 - √ 3 ) * ( 2√ 7 + 3√ 3 ) = b) (5 - 3√ 5 ) * ( 2√ 5 - 4 ) =

(√ 7 - √ 3 ) * ( 2√ 7 + 3√ 3 ) = 2*7 + 3√21 - 2√21 - 3*3 = 14 + √21 -9 = 5 + √21 (5 - 3√ 5 ) * ( 2√ 5 - 4 ) = 2*5 - 20 - 6*5 + 12√5 = 10-20 -30+12√5 = -40 +12√5