Упр.45 ГДЗ Муравин 7 класс (Алгебра)

1) 8a + 120 при a = -9;
2) 5c — 111 при c = -4;
3) 5,71x — 0,71x при x = 0,09;
4) 1,42y + 0,38y при y = -100;
5) 13/16 — (c — 3/4) при c = 9/16;
6) 2b + 5/21 — 17/35 при b = 11/35;
7) 12(2x + 3y) при x = 2/3, y = 3/4;
8) (14a — 63b) : 7 при a = 1/2, b = -1/18.

1. При $$a=-9$$:

   $$8a+120=8\cdot(-9)+120=-72+120=48.$$

2. При $$c=-4$$:

   $$5c-111=5\cdot(-4)-111=-20-111=-131.$$

3. При $$x=0{,}09$$:

   $$5{,}71x-0{,}71x=5x=5\cdot0{,}09=0{,}45.$$

4. При $$y=-100$$:

   $$1{,}42y+0{,}38y=1{,}8y=1{,}8\cdot(-100)=-180.$$

5. При $$c=\frac{9}{16}$$:

   $$ \frac{13}{16}-\left(c-\frac{3}{4}\right) =\frac{13}{16}-\left(\frac{9}{16}-\frac{3}{4}\right) =\frac{13}{16}-\left(\frac{9}{16}-\frac{12}{16}\right) =\frac{13}{16}+\frac{3}{16}=1. $$

6. При $$b=\frac{11}{35}$$:

   $$ 2b+\frac{5}{21}-\frac{17}{35} =2\cdot\frac{11}{35}+\frac{5}{21}-\frac{17}{35} =\frac{22}{35}-\frac{17}{35}+\frac{5}{21} =\frac{5}{35}+\frac{5}{21} =\frac{1}{7}+\frac{5}{21} =\frac{3}{21}+\frac{5}{21} =\frac{8}{21}. $$

7. При $$x=\frac{2}{3},\ y=\frac{3}{4}$$:

   $$ 12(2x+3y)=12\left(2\cdot\frac{2}{3}+3\cdot\frac{3}{4}\right) =12\left(\frac{4}{3}+\frac{9}{4}\right) =12\left(\frac{16}{12}+\frac{27}{12}\right) =12\cdot\frac{43}{12}=43. $$

8. При $$a=\frac{1}{2},\ b=-\frac{1}{18}$$:

   $$ (14a-63b):7 =\left(14\cdot\frac{1}{2}-63\cdot\left(-\frac{1}{18}\right)\right):7 =\left(7+\frac{63}{18}\right):7 =\left(7+\frac{7}{2}\right):7 =\frac{21}{2}:7 =\frac{21}{2}\cdot\frac{1}{7} =\frac{3}{2}=1{,}5. $$

Ответ

1) $$48$$; 2) $$-131$$; 3) $$0{,}45$$; 4) $$-180$$; 5) $$1$$; 6) $$\frac{8}{21}$$; 7) $$43$$; 8) $$1{,}5$$.