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\(\text{1 + 3 - 5 - 7 + 9 + 11 - 13 - 17 + .....+ 393 + 395 - 397 - 399}\)
\(\text{có (399-1) : 2 + 1 = 200 số}\)
\(\text{= (1+3-5-7) + (9+11-13-15) + ..... + (393 + 395 - 397 - 399)}\)
\(\text{= (-8) + (-8) + ... + (-8) }\)
\(\text{có 200 : 4 = 50 số -8}\)
\(\text{= (-8) x 50}\)
\(\text{= -400}\)
b) Đặt 1 + 3 - 5 - 7 + 9 + 11 - .... - 397 - 399 là A ta được:
B = 1 + 3 - 5 - 7 + 9 + 11 - .... - 397 - 399
=> B = ( 1 + 3 - 5 - 7 ) + ( 9 + 11 - 13 - 15 ) + ... + ( 393 + 395 - 397 - 399 )
=> B = ( -8 ) + ( -8 ) + ... + ( -8 )
Vì tổng B có 200 số hạng,4 số hạng tạo thành 1 cặp nên 200 số hạng tạo thành 50 cặp
=> B = ( -8 ) . 50 => B = -400
a) \(9^8=\left(3^2\right)^8=3^{16}\)
\(27^3=\left(3^3\right)^3=3^9\)
\(81^2=\left(3^4\right)^2=3^8\)
\(\Leftrightarrow3^{16}:\left(3^9.3^8\right)\)
\(\Leftrightarrow3^{16}:3^{17}\)
\(\Leftrightarrow3^{-1}=\frac{1}{3}\)
a: 2+4+6+8+...+100
\(=2\left(1+2+\cdots+50\right)\)
\(=2\cdot\frac{50\cdot51}{2}=50\cdot51=2550\)
b: Sửa đề: 1+2-3+4+5-6+...+97+98-99
=(1+2-3)+(4+5-6)+...+(97+98-99)
=0+3+...+96
=3+6+...+96
=3(1+2+...+32)
\(=3\cdot\frac{32\cdot33}{2}=3\cdot16\cdot33=99\cdot16=1584\)
Câu 14:
a. $6.2^2-36:3^2=6.4-36:9=24-4=20$
b. $19.48+52.19-400=19(48+52)-400=19.100-400=1900-400=1500$
Mk thấy bài 1 và 2 dễ nên bạn tự làm nha
3
+)Ta có n-2 \(⋮\)n-2
=>2.(n-2)\(⋮\)n-2
=>2n-4\(⋮\)n-2(1)
+)Theo bài ta có:2n+1\(⋮\)n-2(2)
+)Từ (1) và (2)
=>(2n+1)-(2n-4)\(⋮\)n-2
=>2n+1-2n+4\(⋮\)n-2
=>5\(⋮\)n-2
=>n-2\(\in\)Ư(5)={\(\pm\)1;\(\pm\)5}
+)Ta có bảng:
| n-2 | -1 | 1 | -5 | 5 |
| n | 1\(\in\)Z | 3\(\in\)Z | -3\(\in\)Z | 7\(\in\)Z |
Vậy n\(\in\){1;3;-3;7}
Chúc bn học tốt
a. 5.(–8).( –2).(–3) b. 4.(–5)2 + 2.(–5) – 20
=(-5).8.(-2).(-3) ={(-5).2} {4+1}-20
=(-5)(-2)(-3).8 =(-10).5-20=-50-20=-70
=10.(-24)=-240
a) 4 + ( -1 ) 3 = 4 + ( -1 ) = 3
b ) \(\left(-\frac{1}{4}+\frac{5}{8}\right)+\left(-\frac{3}{8}\right)=\left(-\frac{2}{8}+\frac{5}{8}\right)-\frac{3}{8}=\frac{3}{8}-\frac{3}{8}=0\)
c) { [ ( -3 )2 . 10 - 2.5 - 100 ] + | -10 |: ( -2 ) } : ( -5 )
={ [ ( -9 . 10 - 10 - 100 ] + 10: ( -2 ) } : ( -5 )
={ [ -90 - 10 - 100 ] + (-5) } : ( -5 )
={ [ -100 - 100 ] + ( -5 ) } : ( -5 )
={ -200 + ( -5 ) } : ( -5 )
= -205 : ( -5 )
= 41
a) 76.12 + 24.12 - 200
= 12.(76+24)-200
= 12.100 -200
= 1200-200 = 1000
b) 3^4 . 36 + 4^3 . 81 -100
= 81.36 + 64.81 -100
= 81.(36+64)-100
=81.100-100
=8100-100 = 8000
a) 76.12 + 24.12 - 200
= 12.( 76+24 ) - 200
= 12.100 - 200
= 1200 - 200 = 1000
b) 3^4 . 36 + 4^3 . 81 - 100
= 81.36 + 64.81 - 100
= 81.(36+64) - 100
=81.100 - 100
=8100 - 100 = 8000
Học tốt!
a) 76 . 12 + 24 . 12 - 200 = 12 . ( 76 + 24 ) - 200 = 12 . 100 - 200 = 1200 - 200 = 1000
b)34. 36 + 43 . 81 − 100 = 81 . 36 + 64 . 81 - 100 = 81 . ( 36 + 64 ) - 100 = 81 . 100 - 100 = 8100 - 100 = 8000
a) 76.12+24.12−20076.12+24.12−200;
=(76+24).12-200
=100.12-200
=1200-200
=1000
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000
a,76.12+24.12−200
=12(76+24)-200
=12.100-200
=1200-200=1000
b) 34.36+43.81−100
=81.36+64.81-100
=81(36+64)-100
=81.100-100
=8100-100=8000
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12 + 24.12 – 200 = 12 . (76 + 24) - 2 . 100
= 12 . 100 - 2 . 100
=(12 - 2) . 100
= 10 . 100 = 1000
b) 34.36+43.81−10034.36+43.81-100
=81.36+64.81−100=81.36+64.81-100
=81.(36+64)−1.100=81.(36+64)-1.100
=81.100−1.100=81.100-1.100
=(81−1).100=(81-1).100
=80.100=80.100
=8000
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000= 1000
b) 34.36+43.81−10034
.36+4
3.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12 + 24.12 – 200
= 12 . (76 + 24) - 2 . 100
= 12 . 100 - 2 . 100
= (12 - 2) . 100
= 10 . 100
= 1000
b) 34.36+43.81−10034.36+43.81-100
=81.36+64.81−100=81.36+64.81-100
=81.(36+64)−1.100=81.(36+64)-1.100
=81.100−1.100=81.100-1.100
=(81−1).100=(81-1).100
=80.100=80.100
=8000
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a) 76.12+24.12−20076.12+24.12−200
=12.(76+24)−200=12.(76+24)−200
=12.100−200=12.100−200
=1200− 200=1000=1200− 200=1000.
b) 34.36+43.81−10034.36+43.81−100
=81.36+64.81−100=81.36+64.81−100
=81.(36+64)−100=81.(36+64)−100
=81.100−100=81.100−100
=8100−100=8000=8100−100=8000.
a/76.12+24.12-200
=12.[76+24]-200
=12.100-200
=1200-200
=1000
b/34.36+43.81-100
=81.36+64.81-100
=81.[36+64]-100
=8100-100
=8000
1