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11 tháng 11 2021
Câu 2.
Tóm tắt: \(m=2kg;\Delta l=10cm;g=10\)m/s2
\(F_{đh}=?;k=?\)
Bài giải:
Lực đàn hồi:
\(F=P=mg=2\cdot10=20N\)
Hệ số lực đàn hồi:
\(k=\dfrac{F}{\Delta l}=\dfrac{20}{0,1}=200\)N/m
giup minh vs minh cam on a
6 tháng 3 2022
Theo Vi-ét:\(\left\{{}\begin{matrix}x_1+x_2=\dfrac{1}{2}\\x_1x_2=-2\end{matrix}\right.\)
\(A=3-x_1^2-x_2^2\\ =3-\left(x_1^2+x_2^2\right)\\ =3-\left[\left(x_1+x_2\right)^2-2x_1x_2\right]\\ =3-\left[\left(-\dfrac{1}{2}\right)^2-2.\left(-2\right)\right]\\ =3-\left(\dfrac{1}{4}+4\right)\\ =3-\dfrac{17}{4}\\ =-\dfrac{5}{4}\)
\(B=\left(x_1-x_2\right)^2\\ =x_1^2+x_2^2-2x_1x_2\\ =\left(x_1+x_2\right)^2-4x_1x_2\\ =\left(\dfrac{1}{2}\right)^2-4.\left(-2\right)\\ =\dfrac{1}{4}+8\\ =\dfrac{33}{4}\)
\(D=\left(1+x_1\right)\left(2-x_1\right)+\left(1+x_2\right)\left(2-x_2\right)\\ =2+x_1-x_1^2+2+x_2-x_2^2\\ =4+\left(x_1+x_2\right)-\left(x_1^2+x_2^2\right)\\ =4+\dfrac{1}{2}-\left[\left(x_1+x_2\right)^2-2x_1x_2\right]\\ =\dfrac{9}{2}-\left[\left(\dfrac{1}{2}\right)^2-2.\left(-2\right)\right]\\ =\dfrac{9}{2}-\dfrac{17}{4}\\ =\dfrac{1}{4}\)
NM
7
26 tháng 2 2018
- 1999 . 19981998 + 19991999 . 1998
= - 1999 . 1998 . 10001 + 1999 . 10001 . 1998
= 10001 . 1998 ( - 1999 + 1999 )
= 10001 . 1998 . 0
= 0
TP
16 tháng 11 2021
25. Hợp chất khí với H của 1 nguyên tố là \(RH_3\)
=> Chọn C. Oxit cao nhất của R là \(R_2O_5\), oxit axit
26. R nằm ở nhóm IA
=> Chọn B. R có tính kim loại
27. Cấu hình e: \(1s^22s^22p^63s^23p^2\)
=> R thuộc nhóm IVA
=> Công thức oxit cao nhất: \(RO_2\)
=> Chọn C
sau đăng nhớ tách bài ra nhé
Ex 1
1 am
2 doesn't study
3 aren't
4 Does he have
5 have
6 Does she live
7 are
8 Does my sister work
9 Do dogs like
10 lives
11 rains
12 fly
13 doesn't fry
14 closes
15 tries - don't think
16 passes
17 is - watch
18 has
19 leaves
20 has to
21 play
22 drinks
23 does she speak
24 are spoken
25 are not polished
26 rains
27 arrives
28 starts
29 come
30 does he do
Ex 2
1 is living
2 isn't having
3 am studying
4 is designing
5 is reading
6 is studying - is listening
7 are running
8 are having
9 is playing
10 are watching
11 is staying
12 is always forgetting
13 is being washed
14 is riding
15 isn't being taken
16 are hanging
Ex 3
1 is listening
2 rains
3 works - isn't working
4 is running - wants
5 speaks - comes
6 is coming- are meeting
7 Do - go - do - stay
8 is holding - smell
9 is snowing - snows
10 swims - doesn't run
11 Do - enjoy - am having
12 don't know
13 are - doing - am staying
14 think - looks
15 live- am staying
16 am driving
17 are lying
18 listen - are - listening
19 doesn't understand - are talking
20 does - weigh - looks
Ex 4
1 stayed
2 didn't go
3 had
4 Was my ...
5 visited
6 felt
7 bought
8 Did Lan and Mai see
9 Did Trung eat
10 Did they talk
11 returned
12 didn't think
13 went
14 drove
15 arrived - was
16 had
17 came
18 told
19 walked
20 visited - was
21 bought
22 moved
23 didn't go
24 Did she get