(2х+1) (х-4)=2x²+x-8x-4=2x²-7x-4
<span>(х-3) (х+5) (х+3) (х-5).= (x</span>²-9<span>)(x</span>²-25<span>)=x</span>⁴-9x²-25x²+225=x⁴-34x²+225<span>
(в-8)² - 2в(7в-8)=в</span>²-16в+64-14в²+16в=-13в²+64=64-13в²<span>
3с(4с+2) - (3+с)²= 12с</span>²+6с-9-6с-с²=11с²-9
Пусть скорость катера по течению х. ⇒
(5/x)+(9*/(x-8))=1
5*(x-8)+9*x=x*(x-8)
5x-40+9x=x²-8x
x²-22x+40=0 D=324 √D=18
x₁=20 x₂=2 ∉
Ответ: скорость катера по течению 20 км/ч.
1) х-у +а(х-у)=(х-у)(1+а)
2)m+n+b(m+n)=(m+n)(1+b)
3)3(m+n)+b(m+n)=(m+n)(3+b)
158.
1) b²-15b+14=b²-14b-b+14=b*(b-14)-(b-14)=(b-14)*(b-1).
2) -x²-6x+7=-(x²+6x-7)=-(x²+6x+x-x-7)=-(x²+7x-x-7)=-(x*(x+7)-(x+7))=
=-(x+7)*(x-1)=(x+7)*(1-x).
3) 30y²-10y-100=10*(3y²-y-10)=10*(3y²-y-5y+5y-10)=10*(3y²-6y+5y-10)=
=10*(3y*(y-2)+5*(y-2))=10*(y-2)*(3y+5).
159.
1) (x²-8x+7)/(x-7)=(x²-7x-x+7)/(x-7)=x*(x-7)-(x-7)/(x-7)=(x-7)*(x-1)/(x-7)=x-1.
2) (4x-8)/(x²-3x+2)=4*(x-2)/(x²-2x-x+2)=4*(x-2)/(x*(x-2)-(x-2))=
=4*(x-2)/((x-2)*(x-1))=4/(x-1).
3) (4x²+x-5)/(16x²-25)=(4x²-4x+4x+x-5)/((4x-5)*(4x+5))=
=(4x²-4x+5x-5)/((4x-5)*(4x+5)=4x*(x-1)+5*(x-1)/((4x-5)*(4x+5))=
=(x-1)*(4x+5)/((4x-5)*(4x+5))=(x-1)/(4x-5).