Bài 2: Tìm x
a) (x-2)2-(2x+3)2=0
b) 9.(2x+1)2-4.(x+1)2=0
c) x3-6x2+9x=0
d) x2.(x+1)-x.(x+1)+x.(x-1)=0
K
Khách
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HB
3
18 tháng 7 2023
A=2(x3-y3)-3(x+y)2
A=2(x-y)(x2+xy+y2)-3(x2+2xy+y2)
A=2.2(x2+xy+y2)-3(x2+2xy+y2)
A=4(x2+xy+y2)-3x2+6xy+3y2
A=4x2+4xy+y2-3x2-6xy+3y2
A=x2-2xy+y2
A=(x-y)2
A= 22
A=4
L
2
NH
18 tháng 7 2023
`n_(P)=(6,2)/31=0,2(mol)`
`n_(O_2)=(4,48)/(22,4)=0,2(mol)`
\(PTHH:4P+5O_2-^{t^o}>2P_2O_5\)
tỉ lệ 4 : 5 : 2
n(mol) 0,2------->0,08
ta có \(\dfrac{n_P}{4}>\dfrac{n_{O_2}}{5}\left(\dfrac{0,2}{4}>\dfrac{0,2}{5}\right)\)
`=>P` dư, `O_2` hết, tính theo `O_2`
`m_(P_2 O_5)=n*M=0,08*142=11,36(g)`
L
0
18 tháng 7 2023
a)x2-6x+9
=x2-2.x.3+32
=(x-3)2
b)4x2+4x+1
=(2x)2+2.2x.1+12
=(2x+1)2
c)4x2+12xy+9y2
=(2x)2+2.2x.3y+(3y)2
=(2x+3y)2
d)4x4-4x2+4
=(2x2)2-2.2x2.2+22
=(2x2-2)2
NA
1
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
18 tháng 7 2023
y2(\(x\) + y) - ( \(x\) - 7)2 (đk \(x\) +y ≥ 0)
= (y\(\sqrt{\left(x+y\right)}\) )2 - (\(x\) - 7)2
= (y\(\sqrt{x+y}\) - (\(x-7\)))( y\(\sqrt{x+y}\) + (\(x\) - 7))
= (y\(\sqrt{x+y}\) - \(x\) + 7)(y\(\sqrt{x+y}\) + \(x\) - 7)
NH
1
KV
18 tháng 7 2023
a) Ta có:
VT = (x - y)² + 4xy
= x² - 2xy + y² + 4xy
= x² + 2xy + y²
= (x + y)²
= VP
b) Ta có:
(x + y)² = (x - y)² + 4xy
= 5² + 4.3
= 25 + 12
= 37
L
19 tháng 7 2023
2. When I (open) opened the door, a friend (stand) was standing there.
3. When I (arrive) arrived In the carpark, my car wasn’t there.
“Oh, what did you(do) do ?” I (report) reported it to the police.
4. We (not see) haven't seen Nga since Monday.
5. Lan (be) has been in the USA for 2 years.
6. I (go) was going to bed at 11 o’clock last night.
7. They (move) moved to London in 2003.
8. They (live) have lived in HCM city since January.
9. Mr. Lam (always/ forget) is always forgetting her things.
10.That’s a very old bike. He (have) has had it for a long time. 11.These machines (work) will have worked very well by the time you come back next month.
12. I (buy) bought the motorbike 5 years ago.
13. Peter (be)has been ill for a week.
14. Hoa (visit) visits her parents once a year.
L
19 tháng 7 2023
15. Will Nam (go) go to West Lake Park on his birthday?
16. What do you often(do) do on your birthday?
17. Hoa and Linh often(play) play badminton after class.
18. Many people in the countryside still (work) work seven days a week.
19. Mai still in her room.She (iron) is ironing her clothesfor next week.
20. The street (become) becomes very crowded after 5 p.m every day.
21. She (come) came to France 2 years ago.
22. I (just send) have just sent a letter.
23. He (work) has worked for that company for 5 years.
24. I (graduate) graduated from Hue University last year.
25. Tom (play) plays football every afternoon.
26. I (cook) was cooking in the kitchen when he came in.
27. Mai (attend) are attending the meeting at the moment.
28. -By the time Sonia got to the party, everyone had begun (begin) dancing.
29. I (help) help him whenever he needs.
(Có thể sai nha)
(Có thể sai nha)
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
18 tháng 7 2023
a : 7 dư 3 cm a2 : 7 dư 2
Ta có: a = 7k + 3
⇔ a2 = (7k + 3)2
⇔ a2 = 49k2 + 42k + 9
⇔ a2 = 7.(7k2 + 6k + 1) + 2
7 ⋮ 7 ⇔ 7.(7k2 + 6k + 1) ⋮ 7
⇔ a2 = 7.(7k2 + 6k + 1) + 2 : 7 dư 2 (đpcm)
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
18 tháng 7 2023
Cách 2 sử dụng đồng dư thức:
a \(\equiv\) 3 (mod 7) ⇔ a2 \(\equiv\) 32 (mod 7) 32 : 7 dư 2 ⇔ a2 : 7 dư 2 (đpcm)
a)\(\left(x-2\right)^2-\left(2x+3\right)^2=0\Rightarrow\left(x-2+2x+3\right)\left(x-2-2x-3\right)=0\)
\(\Rightarrow\left(3x+1\right)\left(-x-5\right)=0\Rightarrow\left[{}\begin{matrix}3x+1=0\\-x-5=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x=-5\end{matrix}\right.\)
b)\(9\left(2x+1\right)^2-4\left(x+1\right)^2=0\Rightarrow\left[3\left(2x+1\right)+2\left(x+1\right)\right]\left[3\left(2x+1\right)-2\left(x+1\right)\right]=0\)
\(\Rightarrow\left[8x+5\right]\left[4x+1\right]=0\Rightarrow\left[{}\begin{matrix}8x+5=0\\4x-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-\dfrac{5}{8}\\x=\dfrac{1}{4}\end{matrix}\right.\)
c)\(x^3-6x^2+9x=0\Rightarrow x\left(x^2-6x+9\right)=0\Rightarrow x\left(x-3\right)^2=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x-3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=3\end{matrix}\right.\)
d) \(x^2\left(x+1\right)-x\left(x+1\right)+x\left(x-1\right)=0\)
\(\Rightarrow x\left(x+1\right)\left(x^2-1\right)+x\left(x-1\right)=0\)
\(\Rightarrow x\left(x+1\right)\left(x-1\right)\left(x+1\right)+x\left(x-1\right)=0\)
\(\Rightarrow x\left(x-1\right)\left[\left(x+1\right)\left(x+1\right)+1\right]=0\)
\(\Rightarrow x\left(x-1\right)\left[\left(x+1\right)^2+1\right]=0\)
Do \(\left(x+1\right)^2+1>0\)
\(\Rightarrow x\left(x-1\right)=0\Rightarrow\left[{}\begin{matrix}x=0\\x-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)