Cho A=\(\frac{1985\text{×}1987-1}{1980+1985\text{×}1986}\)
Hãy so sánh A với 1
Những câu hỏi liên quan
So sánh phân số sau :
1985*1987-1/1980+1985*1986 với 1
tìm x,y,z biết
\(\frac{\text{x-1986 - 1987}}{1985}+\frac{\text{x- 1985 - 1987}}{1986}+\frac{\text{x-1985 - 1986}}{1987}=3\)
nhanh mk tick
\(\frac{x-1986-1987}{1985}+\frac{x-1985-1987}{1986}+\frac{x-1985-1986}{1987}=3\)
=> \(\left(\frac{x-1986-1987}{1985}-1\right)+\left(\frac{x-1985-1987}{1986}-1\right)+\left(\frac{x-1985-1986}{1987}-1\right)=3-3\)
=> \(\frac{x-1985-1986-1987}{1985}+\frac{x-1985-1986-1987}{1986}+\frac{x-1985-1986-1987}{1987}=0\)
=> \(\left(x-1985-1986-1987\right).\left(\frac{1}{1985}+\frac{1}{1986}+\frac{1}{1987}\right)=0\)
=> \(\left(x-5958\right).\left(\frac{1}{1985}+\frac{1}{1986}+\frac{1}{1987}\right)=0\)
Mà \(\frac{1}{1985}+\frac{1}{1986}+\frac{1}{1987}\ne0\)
=> x - 5958 = 0
=> x = 5958
Đúng 0
Bình luận (0)
\(\frac{x-1986-1987}{1985}+\frac{x-1985-1987}{1986}+\frac{x-1985-1986}{1987}=3\)
(x-1986-1987) / 1985 + (x-1985-1987) / 1986 + (x-1985-1986) / 1987 = 3
......................../??????
1 so sánh
a, -36 .85.20 /25.84.34 và -30 .63.65.(-8) /117.(-200).49
b, 1985. 1987 -1/ 1980 +1985 .1986 và 1
c, A= 13^15 +1 /13^16 +1 và B= 13^16 +1/ 13^17 +1
d, 2013/2015 và 2015/2017
e, 69/68 và 72/71
x-1986-1987/1985+x-1985-1987/1986+x-1985-1986/1987=3 . Tim x
(x-1986-1987) / 1985 + (x-1985-1987) / 1986 + (x-1985-1986) / 1987 = 3
giúp mình nha mình tick
Hãy tìm A biết A là số lớn nhất với điều kiện sau:
A\(\le\)B
B=\(\frac{1}{\frac{1}{1985}+\frac{1}{1986}+\frac{1}{1987}+...+\frac{1}{2015}}\)
So sánh hai biểu thức A và B
A=124( 1/1*1985 + 1/2*1986 + 1/3*1987 + ... + 1/16*2000)
B= 1/1*17+ + 1/2*19 + ...+ 1/1984*2000)
Ta có: \(A=124\left(\frac{1}{1.1985}+\frac{1}{2.1986}+\frac{1}{3.1987}+...+\frac{1}{16.2000}\right)\)
\(=\frac{124}{1984}\left(\frac{1984}{1.1985}+\frac{1984}{2.1986}+\frac{1984}{3.1987}+...+\frac{1984}{16.2000}\right)\)
\(=\frac{1}{16}\left(1-\frac{1}{1985}+\frac{1}{2}-\frac{1}{1986}+\frac{1}{3}-\frac{1}{1987}+...+\frac{1}{16}-\frac{1}{2000}\right)\)
\(=\frac{1}{16}\left[\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{16}\right)-\left(\frac{1}{1985}+\frac{1}{1986}+\frac{1}{1987}+...+\frac{1}{2000}\right)\right]\)
\(B=\frac{1}{1.17}+\frac{1}{2.19}+...+\frac{1}{1984.2000}\)
\(=\frac{1}{16}\left(\frac{16}{1.17}+\frac{16}{2.18}+...+\frac{16}{1984.2000}\right)\)
\(=\frac{1}{16}\left(1-\frac{1}{17}+\frac{1}{2}-\frac{1}{18}+...+\frac{1}{1984}-\frac{1}{2000}\right)\)
\(=\frac{1}{16}\left[\left(1+\frac{1}{2}+...+\frac{1}{1984}\right)\right]-\left[\frac{1}{17}+\frac{1}{18}+...+\frac{1}{2000}\right]\)
\(=\frac{1}{16}\left[\left(1+\frac{1}{2}+...+\frac{1}{16}\right)+\left(\frac{1}{17}+\frac{1}{18}+...+\frac{1}{1984}\right)-\left(\frac{1}{17}+\frac{1}{18}+...+\frac{1}{1984}\right)-\left(\frac{1}{1985}+\frac{1}{1986}+...+\frac{1}{2000}\right)\right]\)
\(=\frac{1}{16}\left[\left(1+\frac{1}{2}+...+\frac{1}{16}\right)-\left(\frac{1}{1985}+\frac{1}{1986}+...+\frac{1}{2000}\right)\right]\)
Vậy A = B
Đúng 1
Bình luận (0)
