Question

Упростите выражение left (sqrt{ 7 } - sqrt{ 12 }right ) cdot left (sqrt{ 7 } - 3 sqrt{ 3 }right )

Answer 1

$left (sqrt7-sqrt{12}right )left (sqrt7-3sqrt3right )=(sqrt7-2sqrt3)(sqrt7-3sqrt3)=\\=7-3sqrt{21}-2sqrt{21}+6cdot 3=25-5sqrt{21}$