b, \(\dfrac{56\cdot2+56\cdot3}{15\cdot56}=\dfrac{56\cdot\left(2+3\right)}{15\cdot56}\)
=\(\dfrac{56\cdot5}{15\cdot56}=\dfrac{1}{3}\)
c, \(\dfrac{20082008}{20112011}=\dfrac{2008\cdot10001}{2011\cdot10001}=\dfrac{2008}{2011}\)
d, \(\dfrac{2+2}{217\cdot32+217+33}=\dfrac{4}{217\cdot\left(32+33\right)}\)
=\(\dfrac{4}{217\cdot65}=\dfrac{4}{14105}\)
BT: Tìm x, biết:
a) \(2\dfrac{2}{3}x+3\dfrac{3}{4}x=\dfrac{385}{24}\)
b) \(-2\dfrac{2}{3}:x=1\dfrac{7}{9}:0.8\)
c) \(140\%+\dfrac{5}{3}x+2x=2280\)
d) \(-3\dfrac{1}{3}\cdot\left|x\right|=1\dfrac{1}{2}-2\dfrac{2}{3}\)
Bài 1 Tính
a) ( \(\dfrac{-2}{3}\) + \(1\dfrac{1}{4}\) - \(\dfrac{1}{6}\) ) : \(\dfrac{-24}{10}\)
b) \(\dfrac{13}{15}\) x 0.25 x 3 + ( \(\dfrac{8}{15}\) - \(1\dfrac{19}{60}\) ) \(1\dfrac{23}{24}\)
c) ( \(\dfrac{12}{32}\) + \(\dfrac{5}{-20}\) - \(\dfrac{10}{24}\) ) : \(\dfrac{2}{3}\)
d) \(4\dfrac{1}{2}\) : ( 2.5 - \(3\dfrac{3}{4}\) ) + ( -\(\dfrac{1}{2}\) )
e) \(\dfrac{-5}{2}\) : ( \(\dfrac{3}{4}\) - \(\dfrac{1}{2}\) )
Bài 1:
a, Cho A = \(\dfrac{1}{2^2}+\dfrac{1}{4^2}+\dfrac{1}{6^2}+....+\dfrac{1}{100^2}\)
Chứng tỏ: A <\(\dfrac{1}{2}\)
b, Cho B = \(\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+....+\dfrac{1}{2^{20}}\)
Chứng tỏ B < 1
c, Cho C = \(\dfrac{1}{5}+\dfrac{1}{13}+\dfrac{1}{14}+\dfrac{1}{15}+\dfrac{1}{61}+\dfrac{1}{62}+\dfrac{1}{63}\)
Chứng tỏ C < \(\dfrac{1}{2}\)
d, Cho D = \(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{20^2}\)
Chứng tỏ D < 1
1)tìm x
a)\(\dfrac{x^2}{6}=\dfrac{24}{25}\)
b)\(\dfrac{x-1}{x+5}=\dfrac{6}{7}\)
c)\(\dfrac{x-2}{x-1}=\dfrac{x+4}{x+7}\)
2)tìm 2 số x,y biết
\(\dfrac{x}{7}=\dfrac{y}{13}\)và x+y =40
3)chứng minh rằng
tỉ lệ thức \(\dfrac{a}{b}=\dfrac{c}{d}\)(b,d khác 0)
ta suy ra được \(\dfrac{a}{b}=\dfrac{a+c}{b+d}\)
giúp mình nhé giải rõ giùm mình mai đi học rồi!
1.Tính
a) (\(\dfrac{-2}{3}\)+1\(\dfrac{1}{4}\)-\(\dfrac{1}{6}\)).\(\dfrac{-24}{10}\)
b) \(\dfrac{13}{15}\).0,25.3+(\(\dfrac{8}{15}\)-\(1\dfrac{19}{60}\)):\(1\dfrac{23}{24}\)
c) (\(\dfrac{12}{32}\)+\(\dfrac{5}{-20}\)-\(\dfrac{10}{24}\)):\(\dfrac{2}{3}\)
d) \(4\dfrac{1}{2}\):(2,5-\(3\dfrac{3}{4}\))+(\(\dfrac{-1}{2}\))\(^2\)
e) \(\dfrac{-5}{2}\):(\(\dfrac{3}{4}\)-\(\dfrac{1}{2}\))
2. Tính nhanh
a) \(\dfrac{5}{23}\).\(\dfrac{17}{26}\)+\(\dfrac{5}{23}\).\(\dfrac{10}{26}\)-\(\dfrac{5}{23}\)
b) \(\dfrac{1}{7}\).\(\dfrac{5}{9}\)+\(\dfrac{5}{9}\).\(\dfrac{2}{7}\)+\(\dfrac{5}{9}\).\(\dfrac{1}{7}\)+\(\dfrac{5}{9}\).\(\dfrac{3}{7}\)
tìm các số nguyên x, y biết
a, \(\dfrac{24}{7x-3}\)=\(\dfrac{-4}{25}\)
b, \(\dfrac{4}{x-6}\)=\(\dfrac{y}{24}\)=\(\dfrac{-12}{18}\)
c, \(\dfrac{-1}{5}\)<\(\dfrac{x}{8}\)<\(\dfrac{1}{4}\)
d, \(\dfrac{x+46}{20}\)=x\(\dfrac{2}{5}\)
f, y\(\dfrac{5}{y}\)=\(\dfrac{86}{y}\)
1. Tính ( hợp lí nếu có thể )
a) \(\dfrac{5}{11}+\dfrac{23}{29}+\dfrac{17}{11}\) d)\(\dfrac{-21}{10}+\dfrac{21}{10}\times\dfrac{3}{4}-\dfrac{3}{4}\)
b) \(\dfrac{17}{5}\left(5+\dfrac{2}{7}\right)+\dfrac{47}{7}\)x\(\dfrac{17}{5}\) e) \(2-1,6:\left(1+\dfrac{2}{3}\right)+4\%\)
c)\(10\dfrac{3}{7}-\left(2\dfrac{1}{8}+4\dfrac{3}{7}\right)\)
2. Tìm x, biết:
a)\(\dfrac{2}{3}+x=-45\%\) d)\(3\)-/x-\(\dfrac{1}{2}\)/=\(\dfrac{1}{2}\)(/../giá trị tuyệt đối...)
b)\(x+\dfrac{2}{3}x-\dfrac{4}{5}x=2\dfrac{1}{2}\) e)\(\dfrac{15}{x}-\dfrac{1}{3}=\dfrac{28}{51}\)
c)\(45:\left(3x-4\right)=3^2\)
3.Một khu cườn hình chữ nhật có chiều dài 60 m. Chiều rộng bằng \(\dfrac{3}{4}\) chiều dài
a) Tính diện tích đám đất
b) Người ta để \(\dfrac{7}{9}\) diện tích đám đất trồng cây ăn quả. 30% diện tích còn lại đào ao thả cá. Tính diện tích đào ao thả cá
4. Trên nữa mặt phẳng bờ chứa tia Ox và hai tia Oy và Oz sao cho góc xOy=100o, xOz=20o.
a)Tính góc yOz
b)Vẽ Om là tia phân giác yOz. Tính xOm
\(CMR:\) Từ tỉ lệ thức \(\dfrac{a}{b}=\dfrac{c}{d}\) ta \(\Rightarrow\) được tỉ lệ thức:
\(\dfrac{a^2+b^2}{c^2+d^2}=\dfrac{b^2}{d^2}\)
a)x=\(\dfrac{1}{4}+\dfrac{2}{13}\)
b)\(\dfrac{x}{3}=\dfrac{2}{3}+\dfrac{-1}{7}\)
c)\(\dfrac{-8}{3}+\dfrac{-1}{3}\le x\le\dfrac{-2}{7}+\dfrac{-5}{7}\)
d)\(\dfrac{-5}{6}+\dfrac{8}{3}\dfrac{29}{-x}\le x\le\dfrac{-1}{2}+2+\dfrac{5}{2}\)
