<span><span>5*(c+3)</span> = <span>8*(10-c)</span> -одинаковые знаменатели сокращаются.</span>
<span> 6 6</span>
<span>
</span>
<span>5(с+3)=8(10-с)</span>
<span>5с+15=80-8с</span>
<span>5с+8с=80-15</span>
<span>13с=65</span>
<span>с=65:13</span>
<span>с=5</span>
А = 4-5b. 3 ( 4 - 5b) +7b -8 = 0
12 - 15b +7b -8 = 0
- 8b + 4 = 0
- 8b = 4
b = 1/2
a = 4 - 5 * 0.5
a = 1.5
13 в кубе будет 2197. Нужно 13х13х13 = 2197