1) \(\left(+15\right)+\left(+17\right)=15+17=32\)

2) \(\left(-3\right)+\left(-7\right)=-3-7=-\left(3+7\right)=-10\)

3) \(\left(-25\right)+\left(+4\right)=-25+4=-\left(25-4\right)=-21\)

4) \(\left(-6\right)+\left(-54\right)=-6-54=-\left(6+54\right)=-60\)

5) \(\left(-15\right)+20=20-15=5\)

6) \(\left(-5\right)+8+7+5\)

\(=\left(-5+5\right)+\left(8+7\right)\)

\(=15\)

7) \(\left(-8\right)+\left(-11\right)+\left(-2\right)\)

\(=\left[\left(-8\right)+\left(-2\right)\right]+\left(-11\right)\)

\(=\left(-10\right)+\left(-11\right)\)

\(=-21\)

8) \(15+\left(-5\right)+\left(-14\right)+\left(-16\right)\)

\(=\left[15+\left(-5\right)\right]+\left[\left(-14\right)+\left(-16\right)\right]\)

\(=10+\left(-30\right)\)

\(=-20\)

9) \(\left(-20\right)+\left(-14\right)+3+\left(-86\right)\)

\(=\left[\left(-20\right)+3\right]+\left[\left(-14\right)+\left(-86\right)\right]\)

\(=\left(-17\right)+\left(-100\right)\)

\(=-117\)

10) \(\left(-136\right)+123+\left(-264\right)+\left(-83\right)+240\)

\(=\left[\left(-136\right)+\left(-264\right)\right]+\left[123+\left(-83\right)\right]+240\)

\(=\left(-400\right)+40+240\)

\(=\left(-360\right)+240\)

\(=-120\)

11) \(\left(-596\right)+2001+1999+\left(-404+189\right)\)

\(=\left(-596\right)+2001+1999-404+189\)

\(=\left[\left(-596\right)-404\right]+\left(2001+189\right)+1999\)

\(=\left(-1000\right)+2190+1999\)

\(=1190+1999\)

\(=3189\)

12) \(314+\left(-153\right)+64+121+\left(-247\right)+218\)

\(=\left(314+64+121\right)+\left[\left(-153\right)+\left(-247\right)\right]+218\)

\(=\left(378+121\right)+\left(-400\right)+218\)

\(=499-400+218\)

\(=99+218\)

\(=317\)

\(\text{#}Toru\)

= 6,5

\(\left\{189-\left[34+\left(25+5\right)\right]\right\}:20\\ =\left[189-\left(34+25\right)\right]:20\\ =\left(189-59\right):2\\ =130:20\\ =6,5\)

6.5

\(=\left(189-\left(34+15\right)\right)\div20=\left(189-49\right)\div20=140\div20=7\)

=(189 - ( 34 + 15 ) ) : 20 = ( 189 - 49 ) : 20 = 140 : 20 =7 

k nha bạn

\(\left\{189-\left[34+\left(20-5\right)\right]\right\}\div20\)

\(=\left\{189-\left[34+15\right]\right\}\div20\)

\(=\left\{189-49\right\}\div20\)

\(=140\div20\)

\(=7\)

=900

bạn nhé

tk nhé@@@@@@@@@@@@@@

bye

lay but ra tinh la ra ngay

\(189+11+500+200\)

\(=200+500+200\)

\(=200.2+500\)

\(=400+500\)

\(=900\)

6: \(=3\cdot2\sqrt{3}-4\cdot3\sqrt{3}+5\cdot4\sqrt{3}=14\sqrt{3}\)

7: \(=2\sqrt{3}+5\sqrt{3}-4\sqrt{3}=3\sqrt{3}\)

8: \(=2\cdot4\sqrt{2}+4\cdot2\sqrt{2}-5\cdot3\sqrt{2}=\sqrt{2}\)

9: \(=3\cdot2\sqrt{5}-2\cdot3\sqrt{5}+4\sqrt{5}=4\sqrt{5}\)

10: \(=2\cdot2\sqrt{6}-2\cdot3\sqrt{6}+3\sqrt{6}-5\sqrt{6}=-4\sqrt{6}\)

Đăng lần lượt nhiều nhất 3 câu hỏi thôi, chứ đăng nhiều vậy, thấy nhát làm lắm. 

a=99

b-a=11 =>b=99=11 => b=110

b+b=189 =>110+c=189 =>c=79

a+b+b=99+110+79=288

Có: a = 99

=> b - a = 11

= b - 99 = 11

=> b = 11 + 99

b = 110

b + c = 189 

= 110 + c = 189

=> c = 189 - 110

c = 79

Vậy a + b + c = 99 + 110 + 79 = 288

Tổng cả ba là:

    99 + 189 = 288

       Đáp số: 288

`A)15/9=(5 xx 3)/(3 xx 3)=5/3`

`60/(-96)=(5 xx 12)/(12 xx (-8))=-5/8`

`=>5/3=15/9`

Ta thấy trừ cặp `5/3=15/9` thì còn lại không bằng nhau.

`B)60/(-85)=(5 xx 12)/(5 xx (-17))=-12/17`

`-77/56=(7 xx (-11))/(8 xx 7)=-11/8`

`=>-12/17=60/(-85)`

Ta thấy trừ cặp `-12/17=60/(-85)` thì còn lại không bằng nhau.

a) \(\dfrac{15}{9}=\dfrac{5}{3}\)

b) \(-\dfrac{12}{17}=\dfrac{60}{-85}\)

\(B=2\left(a^3+b^3\right)=2\left(a+b\right)^3-6ab\left(a+b\right)=2\cdot\left(-9\right)^3-6\cdot20\cdot\left(-9\right)=-378\)