Tính

\(1-\dfrac{1}{2}+2-\dfrac{2}{3}+3-\dfrac{3}{4}+4-\dfrac{1}{4}-3-\dfrac{1}{3}-2-\dfrac{1}{2}-1\)

a)2x.(x-\(\dfrac{1}{7}\) ) =0

b) \(\dfrac{3}{4}+\dfrac{1}{4}:x=\dfrac{2}{5}\)

c) \(4\dfrac{5}{9}:2\dfrac{5}{18}-7< x< \left(3\dfrac{1}{5}:3,2+4,5.1\dfrac{31}{45}\right)\)

Câu 1:

Tìm x biết:

\(\left(-0,2\right)^x\) = \(\dfrac{1}{25}\)

Câu 2

Cho △ABC có AB = AC, M là trung điểm của BC

a, Chứng minh △AMB = △AMC

b,Từ M kẻ ME ⊥ AB ( E ∈ AB) , MF ⊥ AC ( F ∈ AC ) . Chứng minh AE = AF.

c, Chứng minh: EF // BC

Câu 3

Tìm x, y, z. Biết rằng \(\dfrac{x}{y+z+1}=\dfrac{y}{x+z+1}=\dfrac{z}{x+y-2}=x+y+z\)

Giúp mk vs mn ơi!!!

Tính hợp lí nếu có thể:

a,\(\left(1,2-\sqrt{\dfrac{1}{4}}\right)\) : \(1\dfrac{1}{20}\) + \(\left|\dfrac{3}{4}-1,25\right|\) - \(\left(-\dfrac{3}{2}\right)^2\)

Giúp mk vs mk cần gấp lắm

\(1\dfrac{1}{4}\)-3\(\left(-\dfrac{1}{3}\right)\)2 - \(\left|-\dfrac{1}{2}\right|\)

\(\dfrac{8}{9}\)+ \(\dfrac{15}{23}\)+ \(\dfrac{1}{9}\)+\(\dfrac{-15}{23}\)+\(\dfrac{1}{2}\)

\(9\cdot\left(\dfrac{-1}{3}\right)^3-3\cdot\left(\dfrac{-1}{3}\right)^2+2\cdot\left(\dfrac{-1}{3}\right)+1\)

x-1/2019+x-2/2018=x-3/2017+x-4/2016

Tính nhanh:

a)\(\left(-\dfrac{1}{2}\right)\)-\(\left(-\dfrac{3}{5}\right)\)+\(\left(-\dfrac{1}{5}\right)\)+\(\dfrac{1}{131}\)-\(\left(-\dfrac{2}{7}\right)\)+\(\dfrac{4}{35}\)-\(\dfrac{7}{18}\)

Cho

\(\dfrac{4^x}{2^{x+y}}=8\) và \(\dfrac{9^{x+y}}{3^{5y}}=243\) (x,y \(\in\)N)

Tính xy