(2; 3)
x=2 y=3
7x-by=20
7*2-3b=20
14-3b=20
-3b=20-14
-3b=6
b= -2
Ответ: -2.
-9x^2=-2
x^2=2/9
x=√2/3
x=-√2/3
x1= -√2/3, x2= √2/3
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A+c=-b;
a+b=-c;
b+c=-a;
a)(2(a+b)+2b-3c)/(3(a+b)+4b-7c)=(-2c+2b-3c)/(4b-10c)=(2b-5c)/(2(2b-5c))=1/2;
(a+c+2b)/(a+c+8b)=(-b+2b)/(-b+8b)=b/7b=1/7;
(1/7)/(1/2)=2/7;
b)(3(a+b)+b-7c)/(4(a+b)+b-6c)=(-3c+b-7c)/(-4c+b-6c)=(b-10c)/(b-10c)=1;
(2a+(b+c))/(7a+(b+c))=(2a-a)/(7a-a)=a/6a=1/6;
1/(1/6)=6;
1) 11\6 * 9\10 = 99\60= 1.65