Question

2 УРАВНЕНИЯ ПОМОГИТЕ ПОЖАЛУЙСТА

Answer 1

$\displaystyle\bf\\1)\\\\12x^{2} -(5x^{2} +2xy)-(7x^{2} -4xy)=12x^{2} -5x^{2} -2xy-7x^{2} +4xy=\\\\=\underbrace{(12x^{2} -5x^{2} -7x^{2} )}_{0}+\underbrace{(4xy-2xy)}_{2xy}=2xy\\\\x=0,35 \ \ ; \ \ y=4\\\\2xy=2\cdot 0,35\cdot 4=2,8\\\\2)\\\\(3a^{2} -8ab)+a^{2} -(7ab+4a^{2} )=3a^{2} -8ab+a^{2} -7ab-4a^{2} =\\\\=\underbrace{(3a^{2} +a^{2}-4a^{2} ) }_{0}-\underbrace{(8ab+7ab)}_{15ab}=-15ab\\\\\\a=2\frac{1}{17} =\frac{35}{17} \ \ \ ; \ \ \ b=-2\frac{3}{7} =-\frac{17}{7}$

$\displaystyle\bf\\-15ab=-15\cdot \frac{35}{17} \cdot\Big(-\frac{17}{7} \Big)=15\cdot 5=75$