-20:(13+6*(-3))=-20:(13-18)=-20:(-5)=4
27/100-4/3:8/9=27/100-4/3*9/8=27/100-36/24=27/100-6/4=27/100-150/100=-123/100=-1,23
4) 3,8у+4,22у-у=7,02у
5) 60*25:100=15
6) -4(3х-2)+2(4-3х)=-12х+8+8-6х=-18х+16
40*5:8=25 станиц прочитал ученик
9) 7х+6*(3-4х)=9-8х
7х+18-24х=9-8х
7х+8х-24х=9-18
-9х=-9
х=1
1)12:3 3/8-1 ц1/4:15/32=8/9
1) 12÷3<span>ц3/8</span>=<span>12/1</span>÷3ц<span>3/8</span>=<span>12/1</span>÷<span>3 · 8 + 3 / 8</span>=<span>12/1</span>÷<span>27/8</span>=<span>12/1</span>·<span>8/27</span>=<span>12 · 8 / 1 · 27</span>=<span>96/27</span>=<span>32*3 / 9*3</span>=<span>32/9</span>=3ц<span>5/9
2)</span>1<span>ц1/4</span>÷<span>15/32</span>=<span>1 · 4 + 1/4</span>÷<span>15/32</span>=<span>5/4</span>÷<span>15/32</span>=<span>5/4</span>·<span>32/15</span>=<span>5 · 32/4 · 15</span>=<span>160/60</span>=<span>8 · 20/3 · 20</span>=<span>8/3</span>=2ц<span>2/3
3)</span><span>3ц<span>5/9-</span></span><span>2ц<span>2/3=3ц5/9-2ц6/9=2ц14/9-2ц6/9=8/9
</span></span>
2)1 31/35:(2-8/9:1ц19/45)=<span><span>143/<span>280
</span></span>1)</span>8/9:1ц19/45=8/9*45/64=<span>360/<span>576=5/8
</span></span>2)2-5/8=<span>16/8</span>−<span>5/8=11</span>/8=1ц3/8
3)1ц 31/35:1ц3/8=<span>66/35</span>−<span>11/8=</span><span>528/280</span>−<span>385/280=</span><span>143/280
</span>
3)(1 1/35:4/5-1 8/35)*3 1/3=<span>3ц31/63
</span><span>1) 1ц 1/35:4/5=1ц2/7
2) 1ц2/7-1ц8/35=1ц2/43
</span><span>3) 1ц2/43*3ц1/3=3ц31/63
4)(7-1 5/9:7/24):20/27
=</span>2ц1/4
<span>1)1ц 5/9:7/24=5ц1/3
2) 7-</span>5ц1/3=<span>1ц2/3
</span>3) 1ц2/3:20/27
=2ц1/4
А*б=(а+5)*(б-5)
аб=аб+5б-5а-25
5б-5а=25
5*(б-а)=25
б-а=5
1) 4у - 8 = 4(у - 2) → 4у - 8 ≡ 4у - 8 (тождество)
2) х + (3х - 4) = 3х - 4 → 4х - 4 ≠ 3х - 4 (не тождество)
3) а - b + c = - (b - a - c) → a - b + c ≡ -b + a + c (тождество)
4) 9а - (b+ с) = 9а - b - с → 9а - b - с≡9а - b - с (тождество)
5) 2у - 6 = 2(у - 1) → 2у - 6 ≠ 2у - 2 (не тождество)
6) 2,5х + 1,7у - 3,2х = х → 1,7у - 0,7х ≠ х (не тождество)