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\(a,A=\left\{4;5;6;7;8;9\right\}\\ A=\left\{x\in N|3< x\le9\right\}\\ b,B=\left\{1;2;3;4;5;6;7;8;9;10;11\right\}\\ B=\left\{x\in N\text{*}|x\le11\right\}\\ c,C=\left\{15;16;17;...;48;49\right\}\\ C=\left\{x\in N|15\le x< 50\right\}\)
a) Cách 1 :
\(A=\left\{5;6;7\right\}\)
Cách 2 :
\(A=x\inℕ|4< x\le7\)
b) Cách 1 :
\(A=\left\{1;2;3;4;5;6;7;8;9;10;11;12\right\}\)
Cách 2 :
\(A=x\inℕ^∗|x\le12\)
a) \(A=\left\{4\right\}\)
\(A=\left\{x|x\inℕ;3< x< 5\right\}\)
b) \(B=\left\{10;11\right\}\)
\(B=\left\{x|x\inℕ;10\le x\le11\right\}\)
c) \(C=\left\{0;1;2;3;4;5\right\}\)
\(C=\left\{x|x\inℕ;x\le5\right\}\)
d) \(D=\left\{10;12;14;16\right\}\)
\(A=\left\{x|x\inℕ;x=2k;5\le k\le8;k\inℕ\right\}\)
e) \(E=\left\{1;3;5;7;9;11;13\right\}\)
\(A=\left\{x|x\inℕ;x=2k-1;1\le k< 8;k\inℕ\right\}\)
f) \(F=\left\{4;8;12;16\right\}\)
\(A=\left\{x|x\inℕ;x=4k;1\le k\le4;k\inℕ\right\}\)
a) Cách 1: \(B=\left\{2;5;8;11;...;299\right\}\)
Cách 2: \(B=\left\{x\in N|x=3k+2,k\in N,x\le300\right\}\)
b) \(B=\dfrac{\left(299+2\right)\left(\dfrac{299-2}{3}+1\right)}{2}=15050\)