b, có nghiệm là 1 và -1/3

\(\frac{a^2}{b^2}+\frac{b^2}{a^2}\ge\frac{1}{2}\left(\frac{a}{b}+\frac{b}{a}\right)^2=\frac{1}{2}\left(\frac{a}{b}+\frac{b}{a}\right)\left(\frac{a}{b}+\frac{b}{a}\right)\)

\(=\left(\frac{a}{b}+\frac{b}{a}\right).\frac{1}{2}\left(\frac{a^2+b^2}{ab}\right)\ge\left(\frac{a}{b}+\frac{b}{a}\right).\frac{1}{2}\left(\frac{2ab}{ab}\right)=\frac{a}{b}+\frac{b}{a}\)

Vậy có điều cần cm 

Dấu = xảy ra <=> a = b

\(A=\left(1-\frac{1}{1+2}\right)\left(1-\frac{1}{1+2+3}\right)...\left(1-\frac{1}{1+2+3+...+2016}\right)\)

\(=\left(1-\frac{1}{\frac{2.3}{2}}\right)\left(1-\frac{1}{\frac{3.4}{2}}\right)...\left(1-\frac{1}{\frac{2016.2017}{2}}\right)\)

\(=\left(1-\frac{2}{2.3}\right)\left(1-\frac{2}{3.4}\right)...\left(1-\frac{2}{2016.2017}\right)\)

\(=\frac{2.3-2}{2.3}.\frac{3.4-2}{3.4}...\frac{2016.2017-2}{2016.2017}\)

\(=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}...\frac{2015.2018}{2016.2017}\)

\(=\frac{1}{3}.\frac{2018}{2016}=\frac{2018}{6048}\)

ngày đầu tiên cửa hàng có số tấn gạo là:

(bí)

o x t 40 y 120

a) Trên cùng 1 nửa mặt phẳng có bờ chứa tia OA, có góc AOB<góc AOC ( 60 độ<120 độ) nên tia OB nằm giữa hai tai OA và OC 

Vậy tia OB nằm giữa 2 tia OA và OC

b)  Vì tia OB nằm giữa hai tia OA và OC nên ta có :

                       Góc AOB+góc BOC=Góc AOC

                        60độ +Góc BOC=120độ 

                                  góc BOC=120độ-60độ

                                góc BOC=60độ

c) + Vì tia OD là tai đối của tia OA nên góc AOC và góc DOC là 2 góc kề bù nên DOA=180độ

            Ta có:                Góc AOC+góc DOC=Góc DOA

                                        120độ+ góc DOC= 180 độ

                                                      góc DOC=180độ-120độ

                                                      góc DOC=60độ

 + Vì tia OE là tia phân giác của góc DOC nên:

         EOC=DOC:2= 60độ:2=30độ

  + Ta có:

                góc EOC+góc BOC=EOB

                    30độ+60độ=90độ

      Vậy EOB=90độ

                Bạn tự vẽ hình nha !!

 có 2 loại ròng rọc 

ròng rọc cố định giúp làm thay đổi   của lực kéo so với khi kéo trực tiếp

ròng rọc động giúp làm lực kéo vật lên nhỏ hưn tronhgj lượng của vật

dùng palăng cho phép giảm giảm cường độ lực kéo

mày ko thoát dược đâu con trai to be 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mà thôi

c2 900

c1 : 9,5%

c2: 900

Bài 1  : 

a, \(3x-1=2x+3\)

\(\Leftrightarrow3x-1-2x-3=0\)

\(\Leftrightarrow x-4=0\Leftrightarrow x=4\)

b, \(\left(x+1\right)\left(x+2\right)+\left(x+1\right)\left(2x-11\right)=0\)

\(\Leftrightarrow x^2+2x+x+2+2x^2-11x+2x-11=0\)

\(\Leftrightarrow3x^2-6x-9=0\)

\(\Leftrightarrow3\left(x-3\right)\left(x+1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=3\\x=-1\end{cases}}\)

Đổi 30 phút = 1/2 giờ

Gọi chiều dài quãng đường AB là x ( km , x > 0 )

Vận tốc lúc về = 50 + 10 = 60km/h

Thời gian lúc đi = x/50

Thời gian lúc về = x/60

Thời gian về ít hơn thời gian đi 1/2 giờ

=> Ta có phương trình : \(\frac{x}{50}-\frac{x}{60}=\frac{1}{2}\)

                              <=> \(x\left(\frac{1}{50}-\frac{1}{60}\right)=\frac{1}{2}\)

                              <=> \(x\cdot\frac{1}{300}=\frac{1}{2}\)

                              <=> \(x=150\)( tmđk )

Vậy quãng đường AB dài 150km

Hu hu , sao toàn lớp lớn hơn mình vậy nè ???