bài 1: tính
(2019 – 2018 + 2017 – 2016 + 2015 + ....... – 4 + 3 – 2) x ( 100 – 25 x 2 x 2)
Những câu hỏi liên quan
Tính :A= [(2018/1)+(2017/2)+(2016/3)+(2015/4)+...+(4/2015)+(3/2016)+(2/2017)+(1/2018)]/[(2019/1)+(2019/2)+(2019/3)+(2019/4)+...+(2019/2015)+(2019/2016)+(2019/2017)+(2019/2018)+(2019/2019)]
Tính :A= [(2018/1)+(2017/2)+(2016/3)+(2015/4)+...+(4/2015)+(3/2016)+(2/2017)+(1/2018)]/[(2019/2)+(2019/3)+(2019/4)+(2019/5)+...+(2019/2015)+(2019/2016)+(2019/2017)+(2019/2018)+(2019/2019)]
Cho x,y>0 thỏa mãn
x^2015+y^2015=x^2016+y^2016=x^2017+y^2017
C/m: 1/x^2018+1/y^2018=1/x^2019+1/y^2019
a)A=/x+7/+/x^2-169/-/x-2018/
b)B=[2018/2+2018/3+2028/4+.....+2019/2018]:[1/2018+2/2017+3/2016+......+2018]
x-1/2019+x-2/2018=x-3/2017+x-4/2016
\(\dfrac{x-1}{2019}+\dfrac{x-2}{2018}=\dfrac{x-3}{2017}+\dfrac{x-4}{2016}\)
\(\Leftrightarrow\left(\dfrac{x-1}{2019}-1\right)+\left(\dfrac{x-2}{2018}-1\right)=\left(\dfrac{x-3}{2017}-1\right)+\left(\dfrac{x-4}{2016}-1\right)\)
\(\Leftrightarrow\dfrac{x-2020}{2019}+\dfrac{x-2020}{2018}=\dfrac{x-2020}{2017}+\dfrac{x-2020}{2016}\)
\(\Leftrightarrow\dfrac{x-2020}{2019}+\dfrac{x-2020}{2018}-\dfrac{x-2020}{2017}-\dfrac{x-2020}{2016}\)
\(\Leftrightarrow\left(x-2020\right)\left(\dfrac{1}{2019}+\dfrac{1}{2018}-\dfrac{1}{2017}-\dfrac{1}{2016}\right)=0\)
Mà \(\dfrac{1}{2019}+\dfrac{1}{2018}-\dfrac{1}{2017}-\dfrac{1}{2016}\ne0\)
\(\Leftrightarrow x-2020=0\)
\(\Leftrightarrow x=2020\)
Đúng 0
Bình luận (0)
\(\dfrac{x+1}{2019}+\dfrac{x+2}{2018}=\dfrac{x+3}{2017}+\dfrac{x+4}{2016}\)
\(\Leftrightarrow\left(\dfrac{x+1}{2019}+1\right)+\left(\dfrac{x+2}{2018}+1\right)=\left(\dfrac{x+3}{2017}+1\right)+\left(\dfrac{x+4}{2016}+1\right)\)
\(\Leftrightarrow\dfrac{x+2020}{2019}+\dfrac{x+2020}{2018}-\dfrac{x+2020}{2017}-\dfrac{x+2020}{2016}=0\)
\(\Leftrightarrow\left(x+2020\right)\left(\dfrac{1}{2019}+\dfrac{1}{2018}-\dfrac{1}{2017}-\dfrac{1}{2016}\right)=0\)
\(\Leftrightarrow x=-2020\)(do \(\dfrac{1}{2019}+\dfrac{1}{2018}-\dfrac{1}{2017}-\dfrac{1}{2016}\ne0\))
Đúng 2
Bình luận (0)
\(\Rightarrow\left(\dfrac{x+1}{2019}+1\right)+\left(\dfrac{x+2}{2018}+1\right)=\left(\dfrac{x+3}{2017}+1\right)+\left(\dfrac{x+4}{2016}+1\right)\\ \Rightarrow\dfrac{x+2020}{2019}+\dfrac{x+2020}{2018}=\dfrac{x+2020}{2017}+\dfrac{x+2020}{2016}\\ \Rightarrow\left(x+2020\right)\left(\dfrac{1}{2019}+\dfrac{1}{2018}-\dfrac{1}{2017}-\dfrac{1}{2016}\right)=0\\ \Rightarrow x=-2020\)
Đúng 3
Bình luận (0)
tính tổng sau: 2 + (-3) + 4 + (-5) +...+ 2015 + (-2016) + 2017 + (-2018) + 2019
sai đề r nha pn
ta thấy ở những số đầu số lẻ âm số chẵn dương nhưng ở các số sau thì ngược lại
Đúng 0
Bình luận (0)
Tính tổng: S = 2020 + 2019 – 2018 – 2017 + 2016 + 2015 – 2014 – 2013 + … + 4 + 3 – 2 – 1 . Vậy S = .................
S = 2020 + 2019 - 2018 - 2017 + 2016 + 2015 - 2014 - 2013 + ... + 4 + 3 - 2 - 1
= ( 2020 + 2019 - 2018 - 2017 ) + ( 2016 + 2015 - 2014 - 2013 ) + ... + ( 4 + 3 - 2 - 1 ) (có tất cả 2020 : 4 = 505 nhóm)
= 4 + 4 + ... + 4
= 4. 505 = 2020
Vậy S = 2020.
S= 2020
Bạn huyền đúng rồi đó .
hok tốt
Xem thêm câu trả lời
BÀI 1 RÚT GỌN PHÂN SỐ108 /-180 B/ 200/ 280 C/ -23232323/ 46464646 BÀI 2 TÍNHA 2/ 2.3 + 2/ 3.4 + 2/ 4.5 + ........ + 2/ 99.100B 1/3 + 1/ 3.5 + 1/ 5.7 + ........+ 1/ 2013 .2015 + 1/ 2015 .2017C 1/12 + 1/20 +1/ 30 + .....+ 1/ 506 +1/ 552D 3/4 . 8/9 . 15/16 . 24. 25.........9800/9801BÀI 3: TÌM XA/ 3/ X+2 1/6 B/ -7/ X 3/15 C/ X- 11/8 5/4X BÀI 4: ( 2015/ 2016 + 2016 + 2017 + 2017/ 2018 ). ( 1/2- 1/3- 1/6)HÃY GIẢI GIÚP MÌNH NHANH NHA
Đọc tiếp
BÀI 1 RÚT GỌN PHÂN SỐ
108 /-180 B/ 200/ 280 C/ -23232323/ 46464646
BÀI 2 TÍNH
A= 2/ 2.3 + 2/ 3.4 + 2/ 4.5 + ........ + 2/ 99.100
B= 1/3 + 1/ 3.5 + 1/ 5.7 + ........+ 1/ 2013 .2015 + 1/ 2015 .2017
C= 1/12 + 1/20 +1/ 30 + .....+ 1/ 506 +1/ 552
D= 3/4 . 8/9 . 15/16 . 24. 25.........9800/9801
BÀI 3: TÌM X
A/ 3/ X+2= 1/6 B/ -7/ X= 3/15 C/ X- 11/8 = 5/4X
BÀI 4:
( 2015/ 2016 + 2016 + 2017 + 2017/ 2018 ). ( 1/2- 1/3- 1/6)
HÃY GIẢI GIÚP MÌNH NHANH NHA