`Answer:`

9B.

a. \(\frac{x+81}{19}+\frac{x+82}{18}>\frac{x+84}{16}+\frac{x+85}{15}\)

\(\Leftrightarrow\frac{x+81}{19}+1+\frac{x+82}{18}+1>\frac{x+84}{16}+1+\frac{x+85}{15}+1\)

\(\Leftrightarrow\frac{x+81+19}{19}+1+\frac{x+82+18}{18}+1>\frac{x+84+16}{16}+1+\frac{x+85+15}{15}+1\)

\(\Leftrightarrow\frac{x+100}{19}+\frac{x+100}{18}-\frac{x+100}{16}-\frac{x+100}{15}>0\)

\(\Leftrightarrow\left(x+100\right)\left(\frac{1}{19}+\frac{1}{18}-\frac{1}{16}-\frac{1}{15}\right)>0\)

Mà \(\frac{1}{19}+\frac{1}{18}-\frac{1}{16}-\frac{1}{15}< 0\)

\(\Rightarrow x+100< 0\Leftrightarrow x< -100\)

b. \(\frac{x-22}{8}+\frac{x-21}{9}+\frac{x-20}{10}+\frac{x-19}{11}< 4\)

\(\Leftrightarrow\left(\frac{x-22}{8}-1\right)+\left(\frac{x-21}{9}-1\right)+\left(\frac{x-20}{10}-1\right)+\left(\frac{x-19}{11}-1\right)< 4-1-1-1-1\)

\(\Leftrightarrow\frac{x-22-8}{8}+\frac{x-21-9}{9}+\frac{x-20-10}{10}+\frac{x-19-11}{11}< 0\)

\(\Leftrightarrow\frac{x-30}{8}+\frac{x-30}{9}+\frac{x-30}{10}+\frac{x-30}{11}< 0\)

\(\Leftrightarrow\left(x-30\right)\left(\frac{1}{8}+\frac{1}{9}+\frac{1}{10}+\frac{1}{11}\right)< 0\)

Mà \(\frac{1}{8}+\frac{1}{9}+\frac{1}{10}+\frac{1}{11}>0\)

\(\Rightarrow x-30< 0\Leftrightarrow x< 30\)

\(a>b\Leftrightarrow-6a< -6b\Leftrightarrow-6a+1< -6b+1\)

Bạn thử làm ngược lại xem ?!

`Answer:`

\(\left|2x-4\right|-5x=12\)

\(\Rightarrow\left|2x-4\right|=5x+12\)

Ta có:

\(\left|2x-4\right|=2x-4\Leftrightarrow2x-4\ge0\) hay \(x\ge2\)

\(\left|2x-4\right|=-2x+4\Leftrightarrow2x-4< 0\) hay \(x< 2\)

Với `x>=2:`

\(2x-4=5x+12\)

\(\Leftrightarrow2x-5x=4+12\)

\(\Leftrightarrow-3x=16\)

\(\Leftrightarrow x=-\frac{16}{3}\text{(Loại)}\)

Với `x<2:`

\(-2x+4=5x+12\)

\(\Leftrightarrow-2x-5x=-4+12\)

\(\Leftrightarrow-7x=8\)

\(\Leftrightarrow x=-\frac{8}{7}\)

là hinh học hay là linh tinh vậy bn?

Là sao vậy ạ, nhìn chả hiều gì cả.

`Answer:`

a) \(3x+15=0\)

\(\Leftrightarrow3x=-15\)

\(\Leftrightarrow x=-5\)

b) \(2\left(x-3\right)=x+4\)

\(\Leftrightarrow2x-6=x+4\)

\(\Leftrightarrow2x-x=4+6\)

\(\Leftrightarrow x=10\)

c) \(x^2-9=\left(2x-1\right)\left(x+3\right)\)

\(\Leftrightarrow\left(x-3\right)\left(x+3\right)=\left(2x-1\right)\left(x+3\right)\)

\(\Leftrightarrow\left(x-3\right)\left(x+3\right)-\left(2x-1\right)\left(x+3\right)=0\)

\(\Leftrightarrow\left(x+3\right)\left(x-3-2x+1\right)=0\)

\(\Leftrightarrow\left(x+3\right)\left(-x-2\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x+3=0\\-x-2=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-3\\-x=2\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-3\\x=-2\end{cases}}}\)

d) \(\frac{x+2}{x-2}-\frac{1}{x}=\frac{2}{x^2-2x}\left(ĐK:x\ne0;x\ne2\right)\)

\(\Leftrightarrow\frac{x\left(x+2\right)}{x\left(x-2\right)}-\frac{x-2}{x\left(x-2\right)}=\frac{2}{x\left(x-2\right)}\)

\(\Rightarrow x\left(x+2\right)-x+2=2\)

\(\Leftrightarrow x^2+2x-x+2-2=0\)

\(\Leftrightarrow x^2+x=0\)

\(\Leftrightarrow x\left(x+1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x+1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\text{(Loại)}\\x=-1\end{cases}}}\)

Tôi không biết gì cả

Số số hạng của dãy tính là:

    ( 41080 - 1 ) : 1 + 1 = 41080(số)

Tổng dãy số là:

    ( 1 + 41080 ) x ( 41080 : 2) = 843 803 740

              Đáp số:843 803 740

Đây là toán lớp 4 nâng cao nhé