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a.

\(x\left(x-1\right)\left(x+1\right)\left(x+2\right)=24\)

\(\Leftrightarrow x\left(x+1\right).\left(x-1\right)\left(x+2\right)-24=0\)

\(\Leftrightarrow\left(x^2+x\right)\left(x^2+x-2\right)-24=0\)

Đặt \(a=x^2+x-1\) , ta có pt:

\(\left(a+1\right)\left(a-1\right)-24=0\)

\(\Leftrightarrow a^2-1-24=0\)

\(\Leftrightarrow a^2-25=0\)

\(\Leftrightarrow\left(a-5\right)\left(a+5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}a=5\\a=-5\end{matrix}\right.\)

*Với a = 5 ta được:

\(x^2+x-1=5\)

\(\Leftrightarrow x^2+x-6=0\)

\(\Leftrightarrow x^2+3x-2x-6=0\)

\(\Leftrightarrow\left(x^2+3x\right)-\left(2x+6\right)=0\)

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

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

\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=2\end{matrix}\right.\)

*Với a = -5 ta được:

\(x^2+x-1=-5\)

\(\Leftrightarrow x^2+x+4=0\)

\(\Leftrightarrow x^2+2.x.\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{15}{4}=0\)

\(\Leftrightarrow\left(x+\dfrac{1}{2}\right)^2+\dfrac{15}{4}=0\) ( loại)

Vậy pt có tập nghiệm là: \(s=\left\{-3;2\right\}\)

c)(ĐKXĐ: x khác 30;29)

\(\Leftrightarrow\dfrac{x-29}{30}-1+\dfrac{x-30}{29}-1=\dfrac{29}{x-30}-1+\dfrac{30}{x-29}-1\)

\(\Leftrightarrow\dfrac{x-59}{30}+\dfrac{x-59}{29}=\dfrac{x-59}{30-x}+\dfrac{x-59}{29-x}\)

\(\Leftrightarrow x=59\)(tm) or \(\dfrac{1}{30}+\dfrac{1}{29}-\dfrac{1}{30-x}-\dfrac{1}{29-x}=0\)

\(\Leftrightarrow\dfrac{-x}{30\left(30-x\right)}+\dfrac{-x}{29\left(29-x\right)}=0\)

\(\Leftrightarrow x=0\)(tm) or \(\dfrac{1}{30\left(30-x\right)}+\dfrac{1}{29\left(29-x\right)}=0\)

\(\Leftrightarrow1741-59x=0\)

\(\Leftrightarrow x=\dfrac{1741}{59}\left(tm\right)\)

Vậy S={0;\(\dfrac{1741}{59}\);59}

Giá trị biểu thức là 930 nha bn!!!

Vì giá trị tuyệt đối là số nguyên dương

        Nên số âm của BT A là số dương

             Do đó:A=30+29+...+2+1+1+2+..+29+30

                       A=(1+2+.....+29+30).2

                        A=465.2

                        A=930

Vậy A=930

 A = |-30|+|-29|+...+|-2|+|-1|+|1|+|2|+....+|29|+|30|

= 30 + 29 + ...+ 2+1 + 1 + 2 + ...+ 29 + 30 

= 2 x ( 1+ 2 + ...+ 29 + 30 ) 

= 2 x 465

= 930

A=l-30l + l-29l +...+l-2l+l-1l+l1l+l2l+...+l29l+l30l

=30 + 29 + ...+ 2 + 1 + 1 + 2 +...+29 + 30

=30 . (3 +1) 

=930

a)15/16:3/8x3/4

=15/16:6/16x12/16

=15/16x16/6x12/16

=15/6x12/16

=30/16=15/8

b)5/11x18/29-5/11x8/29+5/11x19/29

=5/11x(18/29-8/29+19/29)

=5/11x1=5/11

mk viết nhầm 19/20 với đúng

\(5-\frac{1}{2}-\frac{5}{6}-\frac{11}{12}-\frac{19}{20}-\frac{29}{30}\)

\(=\left(1-\frac{1}{2}\right)+\left(1-\frac{5}{6}\right)+\left(1-\frac{11}{12}\right)+\left(1-\frac{19}{20}\right)+\left(1-\frac{29}{30}\right)\)

\(=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\)

\(=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{5}-\frac{1}{6}\)

\(=1-\frac{1}{6}\)

\(=\frac{5}{6}\)

Đáp án : \(\frac{5}{6}\)

TK NHA!!