3
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3/7х×5-8/35х=1/5×7-1×35
15х-8х=7-35
7х=-28
х=-4
Vлодки-x
V течения- y
{3(x+y)=90
{5(x-y)=90
{3x+3y=90|*5
{5x-5y=90|*3
+{15x+15y=450
+{15x-15y=270
30x=720:30
x=24
3(24+y)=90
72+3y=90
3y=90-72
3y=18:3
y=6
1)а)=у^+5у-4у-20=у^+у-20;б)15а^+7ав-3в^,2)а)(в+1)(в-3);б)р(m-n)+2(m-n)=(m-n)(р+2);3)6у^+15у-2у-5-6у^+12у=у-5;б)х^+4х-3х-2=х^+х-12;х^+х-12=х^+х-12(доказано)5)х^+6х+х+6=х^+5; 7х=-1;х=-1/7
Lg³x² =8lgx
2lg³x =8lgx
lg³x - 4lgx = 0
lgx · (lg²x - 4) = 0
lgx · (lgx - 2) (lgx + 2) = 0
1) lgx = 0 → x = 1
2) lgx - 2 = 0 → lgx = 2 → x = 100
3) lgx + 2 = 0 → lgx = -2 → x = 0.01
Ответ: 0,01; 1; 100