Question

очень прошу помочь! даю 25 баллов

Answer 1

2)
$a)2b - a + 4b - 7a+ 7 = \\ = 6b - 8a + 7$
б)
$y + 3(x - 2y) = y + 3x - 6y = \\ = - 5y + 3x$
в)
$10n - (5n - 3) + (3n - 1) = \\ 10n - 5n + 3 +3n - 1 = \\ 8n + 2$
3.
а)
$- 8x = 24 \\ x = 24 \div ( - 8) \\ x = - 3$
б)
$3x + 7 = 0 \\ 3x = 0 - 7 = - 7 \\ x = - 7 \div 3 = - \frac{7}{3} = - 2 \frac{1}{3}$
в)
$13 - 5x - 8 + 2x = 0 \\ 5 - 3x = 0 \\ 3x = 5 - 0 = 5 \\ x = \frac{5}{3} = 1 \frac{2}{3}$
Г)
$7x + 1 - 6x - 3 = 5\\ x - 2 = 5 \\ x = 5 + 2 = 7$
$2 \frac{1}{3} ( - 0.7 + 6) - 7 \frac{2}{3} (3 + 0.7) = \\ 2 \frac{1}{3} \times 5 \frac{3}{10} - 7 \frac{2}{3} \times 3 \frac{7}{10} = - 16$
$2 \frac{1}{ 3} \times 5 \frac{3}{10} = \frac{7}{3} \times \frac{53}{10} = \frac{371}{30} = 12 \frac{11}{30}$
$7 \frac{2}{3} \times 3 \frac{7}{10} = \frac{23}{3} \times \frac{37}{10} = \frac{851}{30} = 28 \frac{11}{30}$
$12 \frac{11}{30} - 28 \frac{11}{30} = - 16$

Answer 2

№2

а)$2b-a+5b-7a+7=7b-8a+7$

б)$y + 3(x - 2y) = y + 3x -6y = 3x - 5y$

в)$10n-(5n-3)+(3n-1)=10n-5n+3+3n-1=8n+2$

№3

а)$-8x=24\\8x=-24\\x=-\frac{24}{8}=-3$

б)$3x+7=0\\3x=-7\\x=-\frac{7}{3}=-2\frac{1}{3}$

в)$13-5x=8-2x\\5-3x=0\\5=3x\\x=\frac{5}{3}=1\frac{2}{3}$

г)$(7x+1)-(6x+3)=5\\7x+1-6x-3=5\\x-2=5\\x=7$

№4

Пусть первый изготовил a деталей, второй - b.

$\left \{ {{a+b=657} \atop {a=b+63}} \right.\left \{ {{b+63+b=657} \atop {a=b+63}} \right.\left \{ {{2b=594} \atop {a=b+63}} \right.\left \{ {{b=297} \atop {a=297+63}} \right.\left \{ {{b=297} \atop {a=360}} \right.$

№5

$2\frac{1}{3}(-0.7+6)-7\frac{2}{3}(3+0.7)=2\frac{1}{3}*5.3-7\frac{2}{3}*3.7=\frac{7*53}{3*10}-\frac{23*37}{3*10}=-\frac{371-851}{30}=-\frac{480}{30}=-16$

№6

$6(x-1)+3(5-x)=9\\6x-6+15-3x=9\\9x+9=9\\9x=0\\x=0$

№7

Пусть карандашей было a, кистей b, линеек c.

$\left \{ {a+b+c=43 \atop c=b-7} \atop  c=\frac{a}{4}} \right.\left \{ {a+b+b-7=43 \atop c=b-7} \atop  a=4c} \right. \left \{ {4b-28+2b=50 \atop c=b-7} \atop  a=4b-28} \right. \left \{ {6b=78 \atop c=b-7} \atop  a=4(b-7)} \right. \left \{ {b=13 \atop c=b-7} \atop  a=4(b-7)} \right. \left \{ {b=13 \atop c=6} \atop  a=24} \right.$