Bài 1. Tính hợp lý ( nếu có thể): 1) [ (- 2) ^ 2 +7.(-10)]:2+9 2) 2019- lceil157- (357 - 1019) rceil 3) (1173 - 3978) - (173 - 2978) 4) - 113.234 + 129.113 -113.(-105) 5) (2020 - 3257) - (2019 - 3255)
B1 : Tính hợp lý ( nếu có thể ):
a) ( -72 ) . 121 + 27 . ( -121 ) -121
b) 2019 - [ 157 - ( 357 -219 ) ]
c) ( 1732 - 5986 ) - ( 732 - 9286 )
d) 25 . 76 - ( -29 ) . 25 -105 . 125
e) ( 2020 + 3257 ) - ( 2019 + 3255 )
B2 : Tìm x, biết :
a) -32 + 3 . 2x + 3 = 3 . 23
b) -13 + 17 - 117 + 113 - | 5 - x | = -52
c) ( 2x - 12 ) . ( x + 1 ) = 0
d) ( x3 + 1 ) . ( -5 - 5x ) = 0
e) | x | + | x + 2 | = 3x
Tính hợp lí (nếu có thể):
A= -1-2+3+4-5-6+7+8-9-10+...+2019+2020-2021-2022+2023
Lời giải:
$A=(-1-2+3+4)+(-5-6+7+8)+(-9-10+11+12)+...+(-2021-2022+2023+2024)-2024$
$=\underbrace{4+4+...+4}_{506}-2024$
$=4.506-2024=0$
(2020 - 3257) - (2019 - 3255)
\(...=2020-3257-2019+3255\)
\(=2020-2019-3257+3255\)
\(=1-2=-1\)
Tính hợp lí:
a. A= -1 + 3 - 5 + 7 - 9 +....- 2017 + 2019
b. B= 2 - 4 + 6 - 8 +...+ 2018 - 2020
c. C= 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8+...-111 - 112 + 113 + 114 + 115
c) C= 1+2-3-4+5+6-7-8+...-111-112+113+114+115
ta thấy : 114 chia 4 dư 2 ; 115 chia 4 dư 3
=> C=1+(2-3-4+5)+(6-7-8+9)+...+((110-111-112+113)+114+115
=> C=1+0+0+...+0+229
=> C=300
1.Tính hợp lí ( nếu có thể)
a, (-243+345) - (257+ (-55) - 129)
b,(-2)3 - 45:(-3)2 – (-2019)0.(-1)2019
c, [27.(-67)+33.(-27)]:(-30)
d,(12+22+….+1002).(34-92)
e, 53.47+532-20210
i,38+(-21)+(-58)+(-6)
h,(2020+27)-[2020+(-73)]-129
g,1-3+5-7+9-11+...+2017+2019+2021
2.Thực hiện phép tính
a, 100:{250:[450-(4.53-22.25)]}
b,[(125)3.75-(-175)5]:20162017
Bài 1: Tính giá trị của biểu thức sau
A=1-\(\dfrac{50-\dfrac{4}{2018}+\dfrac{2}{2019}-\dfrac{2}{2020}}{100-\dfrac{8}{2018} +\dfrac{4}{2019}-\dfrac{4}{2020}}\)
B=\(\dfrac{5^{10}.7^3-25^5.49^2}{\left(125.7\right)^3+5^9.14^3}\)
C=\(x^{2020}\)-\(y^{2020}\)+\(xy^{2019}\)-\(x^{2019}\).y+2019 biết x-y=0
Mong mn giúp đỡ
a: \(A=1-\dfrac{2\left(25-\dfrac{2}{2018}+\dfrac{1}{2019}-\dfrac{1}{2020}\right)}{4\left(25-\dfrac{2}{2018}+\dfrac{1}{2019}-\dfrac{1}{2020}\right)}\)
=1-2/4=1/2
b: \(B=\dfrac{5^{10}\cdot7^3-5^{10}\cdot7^4}{5^9\cdot7^3+5^9\cdot7^3\cdot2^3}\)
\(=\dfrac{5^{10}\cdot7^3\left(1-7\right)}{5^9\cdot7^3\left(1+2^3\right)}=5\cdot\dfrac{-6}{9}=-\dfrac{10}{3}\)
c: x-y=0 nên x=y
\(C=x^{2020}-x^{2020}+y\cdot y^{2019}-y^{2019}\cdot y+2019\)
=2019
Tính hợp lý
A,(-5-13): (-6)=
B,12.15-3.5.10=
C,1-3+5-7+9-11+……+2019-2020=
D,1+(-2)+(-3)+4+5+(-6)+(-7)+8….+99-100=
\(a,\left(-5-13\right):\left(-6\right)=\left(-18\right):\left(-6\right)=3\)
\(b,12.15-3.5.10=12.15-15.10=15.\left(12-10\right)=15.2=30\)
\(c,1-3+5-7+9-11+...+2019-2020\)
\(=\left(1-3\right)+\left(5-7\right)+\left(9-11\right)+\dots+\left(2019-2020\right)\)
\(=\left(-1\right)+\left(-1\right)+\left(-1\right)+\dots+\left(-1\right)\) (có 1010 số -1)
\(=-1010\)
d, không biết làm :))
(-5-13):(-6)=(-18):(-6)=3
12.15-3.5.10=180-150=30
Tính hợp lý:
a) A=\(2021^2\)-2020.(2021+1)
b) B=1+2-3-4+5+6-7-8+9+10-...+2018-2019-2020+2021
c) C=\(\dfrac{5.4^{15}.9^9-4.3^{20}.8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)
a)= 2021.2021-2020.(2021+1)
= 2021.(2020+1)-2020.(2021+1)
= (2021.2020)+2021-(2020.2021)-2020
= 1
b) B= (1+2-3-4)+(5+6-7-8)+(9+10-11-12)...........+(2017+2018-2019-2020)+2021
B= -4+(-4)+....................(-4)+2021
B= -4x505+2021
B= -2020 + 2021
B = 1
Tính S= 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - ... + 2018 - 2019 - 2020 + 2021
S=1+(2-3)+(-4+5)+(6-7)+(-8+9)+...+(-2020+2021)
S=1-1+1-1+1+...+1
S=1+0+0+...+0
S=1
\(S=1+2-3-4+...+2017+2018-2019-2020+2021\\ S=\left(1+2-3-4\right)+...+\left(2017+2018-2019-2020\right)+2021\\ S=\left(-4\right)+\left(-4\right)+\left(-4\right)+...+-4+2021\\ S=505.\left(-4\right)+2021\\ S=-2020+2021\\ S=1\)