<span>8(10-3х)в2-5(10-3х)-3=0
</span>
<span><span>(10-3х)=t
t>0
8t²-5t-3=0
D=5²-(4*8*-3)=25+96=121
t1=(5+11)/16=1
t2=(5-11)/16=-5/16 Неподходит
10-3x=1
-3x=-11
x=11/3
</span></span>
Цена за поезд - 4500 р. цена на машине - 7*8*30=1680р. ответ: 1680
<span>1) x2+7x+10=0
2x+7x+10=0
9x+10=0
9x=-10
x=(-10)</span>÷9
x=-10/9
<span>2) -x2+8x-52=0
</span>-2x+8x-52=0
6x-52=0
6x=52
x=52÷6
x=26/3
<span>3) -x2-4x-3=0
</span>-2x-4x-3=0
-6x-3=0
-6x=3
6x=-3
x=(-3)÷6
x=-1/2
<span>4) -x2-14-50=0
</span>x=-32
<span>5) x2-12x+29=0
</span>x=29/10
<span>6) -x2+4x+5=0
x=-5/2
</span><span>7) -x2+8x-9=0
x=3/2
</span><span>8) x2-4x-2=0
x=-1
</span><span>9) x2+3x-4=0
x=4/5
</span><span>10) x2-14x+49=0
x=49/12
</span><span>11) x2+4x+20=0
x=-10/3</span>
5а=-85,6-3а
5а+3а=-85,6
8а=-85,6:8
а=-10,7