giúp mik vs sắp phải nộp r
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H
26 tháng 11 2021
9. Has the work been done by him?
10. The boxes were opened and cigarettes were taken out by us
11. She was given a new one
12. He is proved wrong
13. We were promised higher wages
14. This is the third time we have been written to about this by them
15. We were asked to be there at 8 o'clock
16. She is being shown how to do it
NM
8
17 tháng 7 2021
a) Ta có: \(x^2-3=0\)
nên \(x^2=3\)
hay \(x\in\left\{\sqrt{3};-\sqrt{3}\right\}\)
b) Ta có: \(4x^2-9=0\)
\(\Leftrightarrow\left(2x-3\right)\left(2x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{3}{2}\end{matrix}\right.\)
c) Ta có: \(\left(x+2\right)^2-\left(x-2\right)^2=5\)
\(\Leftrightarrow x^2+4x+4-x^2+4x-4=5\)
\(\Leftrightarrow8x=5\)
hay \(x=\dfrac{5}{8}\)
17 tháng 7 2021
d) Ta có: \(\left(x+2\right)^3-x^3+6x^2=7\)
\(\Leftrightarrow x^3+6x^2+12x+8-x^3+6x^2-7=0\)
\(\Leftrightarrow12x^2+12x+1=0\)
\(\Delta=12^2-4\cdot12\cdot1=144-48=96\)
Vì Δ>0 nên phương trình có hai nghiệm phân biệt là:
\(\left\{{}\begin{matrix}x_1=\dfrac{-12-4\sqrt{6}}{24}=\dfrac{-3-\sqrt{6}}{6}\\x_2=\dfrac{-12+4\sqrt{6}}{24}=\dfrac{-3+\sqrt{6}}{6}\end{matrix}\right.\)
e) Ta có: \(\left(x-2\right)^2-\left(x-1\right)\left(x+1\right)=7\)
\(\Leftrightarrow x^2-4x+4-x^2+1=7\)
\(\Leftrightarrow-4x=2\)
hay \(x=-\dfrac{1}{2}\)
25 tháng 7 2021
Xét ΔAMB có
MD là đường phân giác ứng với cạnh AB
nên \(\dfrac{AD}{DB}=\dfrac{AM}{MB}\)(1)
Xét ΔAMC có
ME là đường phân giác ứng với cạnh AC
nên \(\dfrac{AE}{EC}=\dfrac{AM}{MC}\)(2)
Ta có: M là trung điểm của BC(gt)
nên MB=MC(3)
Từ (1), (2) và (3) suy ra \(\dfrac{AD}{DB}=\dfrac{AE}{EC}\)
hay DE//BC(đpcm)
2 tháng 7 2021
a) Ta có: \(P\left(x\right)=7x^3+3x^4-x^2+5x^2-6x^3-2x^4+2017-x^3\)
\(=x^4+4x^2+2017\)
b) Bậc của P(x) là 4
c) Các hệ số của P(x) là 1;4;2017
Hệ số cao nhất là 4
Hệ số tự do là 2017
d) \(P\left(0\right)=0^4+4\cdot0^2+2017=2017\)
\(P\left(1\right)=1^4+4\cdot1^2+2017=1+4+2017=2022\)
\(P\left(-1\right)=\left(-1\right)^4+4\cdot\left(-1\right)^2+2017=1+4+2017=2022\)
e) \(P\left(-a\right)=\left(-a\right)^4+4\cdot\left(-a\right)^2+2017=a^4+4a^2+2017\)
\(P\left(a\right)=a^4+4a^2+2017\)
Do đó: P(-a)=P(a)
12 What do you often do after school?
13 What is he doing now?
14 Where are you often have dinner?
15 What is Lan going to buy
16 Where are they going to stay?
17 Why do you like learning English?
18 How many pens does she want>
19 What does Nam have for for lunch
20 How many books does Ha have in the bags?
12. What do you often do after school?
13. What is he doing now?
14. Where do you often have dinner?
15. What is Lan going to buy?
16. Where are they going to stay?
17. Why do you like learning English?
18. How many pens does she want?
19. What does Nam have for lunch?
20. How many books does Ha have in the bags?