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Bài 2 :
a ) l x l < 3
=> l x l thuộc { 0 ; 1 ; 2 }
=> x thuộc { - 2 ; - 1 ; 0 ; 1 ; 2 }
Vậy x thuộc { - 2 ; - 1 ; 0 ; 1 ; 2 }
Câu 2:
a: (x+3)(y+2)=1
\(\Leftrightarrow\left(x+3;y+2\right)\in\left\{\left(-1;-1\right);\left(1;1\right)\right\}\)
hay \(\left(x,y\right)\in\left\{\left(-4;-3\right);\left(-2;-3\right)\right\}\)
b: (2x-5)(y-6)=17
\(\Leftrightarrow\left(2x-5;y-6\right)\in\left\{\left(1;17\right);\left(17;1\right);\left(-1;-17\right);\left(-17;-1\right)\right\}\)
hay \(\left(x,y\right)\in\left\{\left(3;23\right);\left(11;7\right);\left(2;-11\right);\left(-6;5\right)\right\}\)
c: \(\left(x-1\right)\left(x+y\right)=33\)
\(\Leftrightarrow\left(x-1;x+y\right)\in\left\{\left(1;33\right);\left(33;1\right);\left(-1;-33\right);\left(-33;-1\right);\left(3;11\right);\left(11;3\right);\left(-11;-3\right);\left(-3;-11\right)\right\}\)
hay \(\Leftrightarrow\left(x;x+y\right)\in\left\{\left(2;33\right);\left(34;1\right);\left(0;-33\right);\left(-32;-1\right);\left(4;11\right);\left(12;3\right);\left(-10;-3\right);\left(-2;-11\right)\right\}\)
hay \(\left(x,y\right)\in\left\{\left(2;31\right);\left(34;-33\right);\left(0;-33\right);\left(-32;31\right);\left(4;7\right);\left(12;-9\right);\left(-10;7\right);\left(-2;-9\right)\right\}\)
Bài 2 Tìm x thuộc Z để :
a) | x | < 3
=> x <3
mà x ∈ Z
=> x = {2;1;0;-1...}
b) | x - 4 | < 3
=> x - 4 <3
Mà x ∈ Z
=> x = {6;5;4;3;2;1;0;-1...}
c) | x + 10 | < 2
=> x + 10 < 2
Mà x ∈ Z
=> x = {-7;-6;-5;-4;....}
bài 1
A = 1- 2 + 3 - 4 + 5 - 6 + ..... + 99
ta có :
A = 1 - 2 + 3 - 4 + 5 - 6 + ... + 99
= ( 1-2 ) + (3-4) + .....+( 97 -98 ) + 99
= -1 + -1 +-1 + -1 +... + -1 + 99 ( CO 49 CHU SO -1 )
= -1 * 49 + 99 = -49 +99 = 50
VAY A = 50
Bài 2:
a)|x| < 3
x\(\in\){-2;-1;0;1;2}
b)|x - 4 | < 3
x\(\in\){ 6 ; 5 ; 4 ; 3 ; 2 }
c) | x + 10 | < 2
x\(\in\){ -2 ; -10 }
Bài 1:
A = 1 + 2 - 3 + 4 + 5 - 6 +...+98 - 99
A = (1 + 4 + 7 +...+97) + [(2-3)+(5-6)+...+(98-99)]
A = 1617 + [(-1)+(-1)+...+(-1)]
A = 1617 + (-49)
A = +(1617-49) = A = 1568
B = - 2 - 4 + 6 - 8 + 10 + 12 - .... + 60
B =
2)
a) \(x\in\left\{2;1;0;-1;-2\right\}\)
b) \(x\in\left\{6;-6;5;-5;4\right\}\)
c) \(x\in\left\{-9;-11;-10\right\}\)
3)
\(\left(a;b\right)\in\left\{\left(0;1\right);\left(0;-1\right);\left(1;0\right);\left(-1;0\right)\right\}\)
vi a,b \(\in\)Z
suy ra (a-5).(b+6)\(\in\)Z
\(\Leftrightarrow\)(a-5) va (b+6)\(\in\)U(17)
\(\Leftrightarrow\)(a-5).(b+6)\(=\)1.17\(=\)17.1\(=\)-1.(-17)\(=\)-17.(-1)
lap bang gia tri
con lai thi tuong tu nha b
sai roi