<span>Пошаговое:
</span><span><span>(7+3y-x2y)⋅(-2xy)</span><span>=-<span>(7+<span>3y</span>-<span>x2y</span>)⋅2xy</span></span><span>=-(<span>7+<span>(<span>3-x2</span>)y</span></span>)⋅2xy</span><span>=-(<span>7+<span>y(<span>-x2+3</span>)</span></span>)⋅2xy</span><span>=-<span>(<span>y(-x2+3)+7</span>)⋅2xy</span></span><span>=-(<span><span>y(-x2+3)⋅2xy</span>+<span>7⋅2xy</span></span>)</span><span>=<span>-<span>y(-x2+3)⋅2xy</span>-7⋅2xy</span></span><span>=<span>-<span>2yxy(-x2+3)</span>-14xy</span></span><span>=<span>-14xy-2yxy(-x2+3)</span></span></span>
Y=x-1
x^2-2x+1+x^2-4x+4=9
x^2-6x=4
(x-3)^2=13
x=3+sqrt(13) или x=3-sqrt(13)
y=2+sqrt(13) или y=2-sqrt(13)
60км.
1) 78-63= 15км/ч(разница скоростей)
2) 15•4=60( расстояние через 4 часа)