A³-4a=a(a²-4)=a(a+2)(a-2)
ax²-ay²=a(x²-y²)=a(x+y)(x-y)
3a²-6ab+3b²=3(a²-2ab+b²)=3(a-b)(a-b)=3.(a-b)²
ax²+ax+a=a(x²+x+1)
x²+7x=0, x(x+7)=0, x1=0,x2=-7
x²-25=0, (x+5)(x-5)=0, x1=-5,x2=5
<span>log4(4-x)- log4(4) = log4 ((4-x/4)) = log4 (1-x/4)</span>
1кирпич - х
9х-х=20
8х=20
х=20/8=2,5кг