1) х(у+z)-2y-2z=x(y+z)-(2y+2z)=x(y+z)-2(y+z)=(y+z)(x-2).
2) a(b+c)-b-c=a(b+c)-(b+c)=(b+c)(a-1).
3) a(b-c)-4b+4c=a(b-c)-(4b-4c)=a(b-c)-4(b-c)=(b-c)(a-4).
4) a(a-b)-ac+bc=a(a-b)-(ac-bc)=a(a-b)-c(a-b)=(a-b)(a-c).
5) x(y-z)-y+z=x(y-z)-(y-z)=(y-z)(x-1).
6) 2b(x-y)+y-x=2b(x-y)-(x-y)=(x-y)(2b-1).
7) 5(c-b)+ab-ac=5(c-b)-(ac-ab)=5(c-b)-a(c-b)=(c-b)(5-a).
8) 2(x-c)-bx+bc=2(x-c)-(bx-bc)=2(x-c)-b(x-c)=(x-c)(2-b).
8х-(7х+8)=9;8х-7х-8=9;х=17.Ответ:17
2x - <span> </span><span>песок</span>
<span>5x - </span><span>чернозеm</span>
<span>2x + 5x = 42</span>
<span>7x = 42</span>
<span>x = 6</span>
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</span>
<span>2 * 6 = 12 - pesok</span>
<span>5 * 6 = 30 - chernozem</span>
2x-5y=1
5y=2x-1
y=0,4x-0,2
k=0,4
y=0,4x+b
7=0,4*5+b
b=7-2
b=5
y=0,4x+5