cứu em với mn ơi 

cái này hỏi trời nhá em, tự làm nha, không lươiif

Bài 4:

Gọi ba số cần tìm là a,b,c

Theo đề, ta có: \(\left\{{}\begin{matrix}\dfrac{a}{2}=\dfrac{b}{3}\\\dfrac{a}{4}=\dfrac{c}{9}\end{matrix}\right.\Leftrightarrow\dfrac{a}{4}=\dfrac{b}{6}=\dfrac{c}{9}\)

Đặt \(\dfrac{a}{4}=\dfrac{b}{6}=\dfrac{c}{9}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=4k\\b=6k\\c=9k\end{matrix}\right.\)

Ta có: \(a^3+b^3+c^3=-1009\)

\(\Leftrightarrow64k^3+216k^3+729k^3=-1009\)

\(\Leftrightarrow k=1\)

hay a=4; b=6; c=9

19 Because of his illness, he couldn't come to class

20 Because of her unsatisfactory result, her parents felt disappointed

21 If you revise for your final exam carefully, your result will be bad

22 Two dresses have to be dressed in July

23 She hasn't gont to a club since she graduated from university

24 I wish I could understand this English essay

25 The project must be completed by Thursday 

26 The children are so kind that they help the elderly clean the floor

ĐKXĐ:
1.

\(\left\{{}\begin{matrix}x-1>0\\log_2\left(x-1\right)-1>0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x>1\\x-1>2\end{matrix}\right.\) \(\Leftrightarrow x>3\)

2.

\(\left\{{}\begin{matrix}x-1>0\\x-1\ne1\\\dfrac{x}{2-x^2}>0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x>1\\x\ne2\\\left[{}\begin{matrix}x< -\sqrt{2}\\0< x< \sqrt{2}\end{matrix}\right.\end{matrix}\right.\)

\(\Rightarrow1< x< \sqrt{2}\)

Bài 2: 

a: =>(x+5)(4-x)=0

=>x=4 hoặc x=-5

b: =>2x(2x-1)=0

=>x=0 hoặc x=1/2

c: =>2x(x^2+1)+x^2+1=0

=>(x^2+1)(2x+1)=0

=>2x+1=0

=>x=-1/2

d: Δ=(-3)^2-4*1*4=9-16=-7<0

=>PTVN

a) Qua A kẻ đường thẳng vuông góc với tia DE tại K.

Xét tứ giác AHDK: ^AHD = ^HDK = ^AKD = 90⁰; AH=DH => AHDK là hình vuông

=> ^HAK = 90⁰ và AH=AK

Ta có: ^BAH + ^HAC = ^EAK + ^HAC = 90⁰ => ^BAH = ^EAK

Xét \(\Delta\)AHB và \(\Delta\)AKE có: ^AHB = ^AKE (=90⁰); AH=AK; ^BAH = ^EAK

=> \(\Delta\)AHB = \(\Delta\)AKE (g.c.g) => AB=AE (2 cạnh tương ứng) (đpcm).

b) Xét \(\Delta\)ABE vuông tại A có trung tuyến AM => AM=BE/2. Tương tự: DM=BE/2

=> AM=DM => \(\Delta\)MAH = \(\Delta\)MDH (c.c.c) => ^AHM = ^DHM = ^AHD/2 = 45⁰.

ĐS...

Lỗi ảnh r 

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