Question

знатоки алгебры сюда!

Answer 1

8)
$frac{20x}{2x-a}=7x-1;\ x=3;\ frac{20cdot3}{2cdot3-a}=7cdot3-1;\ frac{60}{6-a}=21-1;\ frac{60}{6-a}=20;\ 60=20cdot(6-a);\ 6-a=3;\ a=6-3=3;\ a=3;$
$frac{20x}{2x-3}=7x-1;\ D(f): 2x-3neq0; 2xneq3; xneqfrac32;\ 20x=(7x-1)cdot(2x-3);\ 20x=14x^2-21x-2x+3=0;\ 14x^2-43x+3=0;\ D=43^2-4cdot3cdot14=1681=(pm41)^2;\ x_1=frac{43-41}{28}=frac{2}{28}=frac{1}{14};\ x_2=frac{43+41}{28}=frac{84}{28}=frac{21}{7}=3;\ x=frac{1}{14}.$


3)
$V_c=15 kmcdot h;\ T=3 h 45 min\ L=27 km\ frac{L}{V_c-V_0}+frac{L}{V_c+V_0}=T;\ Lleft(frac{V_c+V_0+V_c-V_0}{(V_c^2-V_0^2)}right)=T;\ Lfrac{2V_c}{V_c^2-V_0^2}=T;\ V_c^2-V_0^2=frac{L}{T}cdot2V_c;\ V_0^2=V_ccdotleft(V_c-2frac{L}{T}right)=15(15-2frac{27}{3frac34})=15^2-30frac{}{}cdotfrac{27}{frac{15}{4}}=225-27cdot8=\ =225-216=9;\ V_0=3 km/h$
скорость течения реки 3 км/час

Answer 2

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