Question

Помогите пожалуйста с решением.

Answer 1

1.
$frac{1}{ frac{1}{18} - frac{1}{21} } = frac{1}{ frac{7}{126} - frac{6}{126} } = \ = frac{1}{ frac{1}{126} } = 1 div frac{1}{126} = 1 times frac{126}{1} = \ = 126$
12.
$(2x + 3y) {}^{2} - 3x( frac{4}{3} x + 4y) = \ = 4 {x}^{2} + 12xy + 9 {y}^{2} - 4 {x}^{2} - 12xy = \ = 9y {}^{2}$
подставим у=√3
$9 {y}^{2} = 9 times (sqrt{3} {)}^{2} = 9 times 3 = 27$