bạn ơi xem lại đề mk max rút gọn mà nó ra 7-4x là sao

bào nào ??

Chỉ phải làm câu 3 bài 1 thôi nhé !

CChiChỉChỉ 

O3=60

O4=60

O2=120

Ht

 ko hiểu thì bảo mik nha ^^

\(2^4.5-\left[31-9^2\right]=16.5-\left(31-81\right)=80-\left(-50\right)=130\)

\(2^4\).5-[1.31-(13-4)^2]

=16.5-[1.31-81]

=16.5-[31-81]

=16.5-(-50)

=80-(-50)

=130

1)

\(\left(a\right)37+397+3997+39997\)

\(=40-3+400-3+4000-3+40000-3\)

\(=\left(40+400+4000+40000\right)-\left(3+3+3+3\right)\)

\(=44440-12=44428\)

\(\left(b\right)298+2998+29998+299998\)

\(=300-2+3000-2+30000-2+300000-2\)

\(=\left(300+3000+30000+300000\right)-\left(2+2+2+2\right)\)

\(=333300-8=333296\)

\(\left(c\right)9+99+999+9999+99999\)

\(=10-1+100-1+1000-1+10000-1+100000-1\)

\(=\left(10+100+1000+10000+100000\right)-\left(1+1+1+1+1\right)\)

\(=111110-5=111105\)

2)
\(\left(a\right)\left(2+4+6+...+2002+2004+2006\right)-\left(1+3+5+...+2001+2003+2005\right)\)

\(=\left(2-1\right)+\left(4-3\right)+\left(6-5\right)+...+\left(2002-2001\right)+\left(2004-2003\right)+\left(2006-2005\right)\)

\(=1+1+1+...+1+1+1\)( 1003 số 1 )

\(=1003\)

\(\left(b\right)88-87+86-85+84-83+...+6-5+4-3+2-1\)

\(=\left(88-87\right)+\left(86-85\right)+\left(84-83\right)+...+\left(6-5\right)+\left(4-3\right)+\left(2-1\right)\)

\(=1+1+1+...+1+1+1\)( 44 số 1 )

\(=44\)

\(\left(c\right)100-98+96-94+92-90+...+12-10+8-6+4-2\)

\(=\left(100-98\right)+\left(96-94\right)+\left(92-90\right)+...+\left(12-10\right)+\left(8-6\right)+\left(4-2\right)\)

\(=2+2+2+...+2+2+2\) ( 25 số 2 )

\(=50\)

3)

\(\left(a\right)360-357+354-351+348-345+...+312-309+306-303+300-297\)

\(=\left(360-357\right)+\left(354-351\right)+\left(348-345\right)+...+\left(312-309\right)+\left(306-303\right)+\)\(\left(300-297\right)\)

\(=3+3+3+3+3+3+3+3+3+3+3=33\)

\(\left(b\right)2006-1-2-3-4-...-47-48-49-50\)

\(=2006-\left(1+2+3+4+...+47+48+49+50\right)\)

\(=2006-\frac{\left(50+1\right)\left[\left(50-1\right)+1\right]}{2}\)

\(=2006-1275=731\)

\(\left(c\right)280-276+272-268+264-260+...+216-212+208-204+200-196\)

\(=\left(280-276\right)+\left(272-268\right)+\left(264-260\right)+...+\left(216-212\right)+\left(208-204\right)+\)\(\left(200-196\right)\)

\(=4+4+4+4+4+4+4+4+4+4+4=44\)

Cảm ơn bạn nha

\(a.\dfrac{7}{8}+\dfrac{1}{2}\text{=}\dfrac{11}{8}\)

\(b.\dfrac{5}{6}+\left(-2\right)\text{=}\dfrac{-7}{6}\)

\(c.\dfrac{2}{5}+\dfrac{-3}{8}\text{=}\dfrac{1}{40}\)

\(d.\dfrac{5}{7}-\dfrac{3}{8}\text{=}\dfrac{19}{56}\)

\(e.\dfrac{3}{4}-\dfrac{1}{2}+\dfrac{7}{6}\text{=}\dfrac{17}{12}\)

`a. 7/8 + 1/2 = 7/8 + 4/8=(7+4)/8=11/8`

`b. 5/6 + (-2) =5/6 + (-12/6)=-7/6`

`c. 2/5 + -3/8   = 16/40 + (-15/40)=1/40`

`d. 5/7  - 3/8  = 40/56 - 21/56=19/56`

`e. 3/4 - 1/2 +7/6= 3/4 - 2/4 + 7/6= 1/4 + 7/6= 6/24 + 28/24= 34/24=17/12`

\(5a^2+5b^2+8ab-2a+2b+2=0\)

\(\Leftrightarrow4a^2+4b^2+8ab+a^2-2a+1+b^2-2b+1=0\)

\(\Leftrightarrow\left(2a+2b\right)^2+\left(a-1\right)^2+\left(b+1\right)^2=0\)

\(\Leftrightarrow\hept{\begin{cases}2a+2b=0\\a-1=0\\b+1=0\end{cases}\Leftrightarrow\hept{\begin{cases}a\cdot1+2\left(-1\right)=0\left(tm\right)\\a=1\\b=-1\end{cases}}}\)

Thay a, b vào B ta được :

\(B=\left(1-1\right)^{2018}+\left(1-2\right)^{2019}+\left(-1+1\right)^{2020}\)

\(B=0^{2018}+\left(-1\right)^{2019}+0^{2020}\)

\(B=-1\)

Dòng 2 là \(+2b\)nhé mình bấm lộn :)