a chia hết cho 18 và 5 nên a là bội chung của 18 và 15

15= 3.5

18=3^2.2

BCNN ( 15 ,18 ) = 3^2.5.2= 90

suy ra BC( 15,18)= 90; 180; 270; 360 ;450.....

vì 100< hoặc bằng x < hoặc bằng 200 nên a=180

a, A={11,12,13,14,15}

b, B={10,11,12,13,14,15,16,17,18,19,20}

c, C={6,7,8,9,10}

d,D={11,12,13,...,95,96,97,98,99,100}

e, E={2983,2984,2985,2986}

f, F={0,1,2,3,4,5,6,7,8,9}

g, G={0,1,2,3,4}

h, H={0,1,2,3,4,5,6,...,98,99,100}

thank you

e) Ta có : ( x + 1 ) + ( x + 2 ) + ( x + 3 ) + .... + ( x + 100 ) = 5750 

<=> 100x + ( 1 + 2 + 3 + ...... + 100) = 5750

=> 100x + 5050 = 5750

=> 100x = 700

=> x = 7

a) x = 31 ; 32 ; 33 ; 34 ; 35 ; 36 ; 37 ; 38 ; 39

Ta có :

\(B=\left\{x\in N,x=2k\left(k\in N\right);13< x\le56\right\}\)

\(\Rightarrow B=\left\{14;16;18;20;................;56\right\}\)

Vì \(B=\left\{x\in N;x=2k\left(k\in N\right);13< x\le56\right\}\)

\(\Rightarrow B=\left\{14;16;18;20;...;56\right\}\)

\(a,\Rightarrow\left(4x-1\right)^2=25=5^2=\left(-5\right)^2\\ \Rightarrow\left[{}\begin{matrix}4x-1=5\\4x-1=-5\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-1\end{matrix}\right.\\ b,\Rightarrow2^x\left(1+2^3\right)=144\\ \Rightarrow2^x=144:9=16=2^4\Rightarrow x=4\\ c,\Rightarrow3^{2x+3}=3^{2\left(x+3\right)}\\ \Rightarrow2x+3=2x+6\Rightarrow0x=3\left(vô.lí\right)\\ \Rightarrow x\in\varnothing\)