đáp án là 

a) A =(x N|=(x N|108:x,240:x,x>5)

Vì 108:x,240:x, nên  x∈N Ư(108); x∈N Ư(240)

Ta có: Ư(108) = {1;2;3;4;6;9;12;18;36}

          Ư(240) = {1; 2; 3; 4; 5; 6; 8; 10; 12; 15; 20; 30; 40; 60; 120; 240}

mà 108:x,240:x và x > 5 nên x∈{6;12}

Vậy x∈{6;12}

b) B=(x N*|x:4,x:6,x:10và x<200)

Vì x:4,x:6,x:10, nên  x∈N B(4); x∈N(6); x∈N(10)

Ta có: B(4) = {0;4;8;12;16;20;24;28;32;36;40....}

          B(6) = {0;6;12;18;24;30;36;42;48;54;60;66;72;78;.....}

          B(10) = {0;10;20;30;40;50;60;70;80;90;100;1110;....}

=(57-17)+(58-18)+(59-19)+(60-20)+(61-21)

=40+40+40+40+40

=200

275

ngược lại là j

chép đi cháu:

a; \(x\)(2\(x\) - 10) = 0

   \(\left[{}\begin{matrix}x=0\\2x-10=0\end{matrix}\right.\)

     \(\left[{}\begin{matrix}x=0\\2x=10\end{matrix}\right.\)

     \(\left[{}\begin{matrix}x=0\\x=\dfrac{10}{2}\end{matrix}\right.\)

      \(\left[{}\begin{matrix}x=0\\x=5\end{matrix}\right.\)

Vậy \(x\) \(\in\) {0; 5}

b; (\(x+1\)).(\(x-2\)) = 0

   \(\left[{}\begin{matrix}x+1=0\\x-2=0\end{matrix}\right.\)

    \(\left[{}\begin{matrix}x=-1\\x=2\end{matrix}\right.\)

   Vì \(x\) \(\in\) N nên \(x=-1\) loại

Vậy \(x\) = 2

\(x\) + (-36) = 0

\(x-36=0\)

        \(x\) = 36

Vậy \(x=36\)

x-36=0 (phá ngoặc)

x     =0+36

x=36

\(\dfrac{4}{6}+\dfrac{27}{81}=\dfrac{2}{3}+\dfrac{1}{3}=\dfrac{3}{3}=1\)

\(\dfrac{48}{96}-\dfrac{135}{270}=\dfrac{1}{2}-\dfrac{1}{2}=0\)

\(\dfrac{30303}{80808}+\dfrac{303030}{484848}=\dfrac{3}{8}+\dfrac{5}{8}=\dfrac{8}{8}=1\)

c là 23 phần 24

= 20+15

=35

Ê dễ màa :))

Lời giải:

a.

$(5x-6)(1999^2+2.1999+1)=4.10^3$

$(5x-6)(1999+1)^2=(4.10^3)^2=4000^2$
$(5x-6).2000^2=4000^2$

$5x-6=\frac{4000^2}{2000^2}=2^2=4$

$5x=10$

$x=10:5=2$

b.

$(23545-7^5)x:[(8^4-4.10^3)^2-2478]=1$

$6738.x:6738=1$

$x=1$

25 - (\(x-5\))  = - 415 - (15 - 415)

25 - \(x+5\) = - 415 - 15 + 415

(25 + 5) - \(x\) = (-415 + 415) - 15

    30 - \(x\)   = 0 - 15

           \(x\) =  30  -(-15)

           \(x=\) 30 + 15

            \(x=45\)

Vậy \(x=45\)

25-(x-5)=415-(15-415)

=>25-x+5=415-15+415

=>30-x=830-15=815

=>x=30-815=-785