1.Chứng minh rằng:122-124+126-...+124n−2-124n+...+122002-122004<0,2
112+114+116+118+120+122+124+126+148+130
112+114+116+118+120+122+124+126+148+130=1230
chúc bn hok giỏi
112+114+116+118+120+122+124+126+148+130
=1230
đ/s: 1230
Tìm x biết :\(\frac{x+1}{125}+\frac{x+2}{124}+\frac{x+3}{123}+\frac{x+4}{122}+\frac{x+126}{5}=0\)
\(\frac{x+1}{125}+\frac{x+2}{124}+\frac{x+3}{123}+\frac{x+4}{122}+\frac{x+146}{5}=0\)
\(\left(\frac{x+1}{125}+1\right)+\left(\frac{x+2}{124}+1\right)+\left(\frac{x+3}{123}+1\right)+\left(\frac{x+4}{122}+1\right)+\left(\frac{x+146}{5}-4\right)=0\)
\(\frac{x+126}{125}+\frac{x+126}{124}+\frac{x+126}{123}+\frac{x+126}{122}+\frac{x+126}{5}=0\)
\(\left(x+126\right).\left(\frac{1}{125}+\frac{1}{124}+\frac{1}{123}+\frac{1}{122}+\frac{1}{5}\right)=0\)
vì \(\left(\frac{1}{125}+\frac{1}{124}+\frac{1}{123}+\frac{1}{122}+\frac{1}{5}\right)\ne0\)nên x + 126 = 0 \(\Rightarrow\)x = -126
112+114+116+118-120+122+124+126+128
Tính nhanh : [giải ]
=(112+128)+(114+126)+(116+124)+(118+122)+120
=240+240+240+240+120
= 120+120+120+120+120+120+120+120+120
= 120 x 9
= 1080
tich nha ban oi , thanks
=(112+118)+(114+126)+(118+122)+120+116
=230+240+240+120+116
=470+360+116
=830+116
=946
112+114+116+118+120+122+126+128
=(112+128)+(114+126)+(118+122)+120+116
=240+240+240+120+116
=240x3+120+116
=720+120+116
=840+116
=956
Chứng minh rằng với số tự nhiên n > 2 thì không là số tự nhiên
Trong các số tự nhiên liên tiếp sau, số chia cho 10 còn dư 7 là số nào?
119; 120; 121; 122; 123; 124; 125; 126; 127; 128
Tìm x
a) X x 15 + X x 13 = 560 x 45
( X + X x 2 ) : 34 = 504
360 : X - 126 = X = 6
58 x X - 934 = 6722
14968 - X x 5 = 4968
b) X x 125 - X x 73 = 1196
246 : X = 34 : X = 5
2005 + X x 34 = 5337
X : 1234 = 127 ( dư 360 )
Chứng minh rằng S = 1 2 + 1 2 2 + 1 2 3 + . . . + 1 2 20 < 1
Chứng minh rằng D = 1 2 2 + 1 3 2 + 1 4 2 + . . . + 1 10 2 < 1