Cứu em với ạ.Em cảm ơn
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Câu 2:
a: \(=xy^5\cdot\dfrac{1}{4}x^6\cdot\left(-8\right)y^3z^3=-2x^7y^8z^3\)
b: \(f\left(1\right)=3\cdot1^2-4+1=0\)
=>x=1 là nghiệm của f(x)
\(f\left(-\dfrac{1}{3}\right)=3\cdot\dfrac{1}{9}-4\cdot\dfrac{-1}{3}+1=\dfrac{1}{3}+\dfrac{4}{3}+1=\dfrac{8}{3}\)
=>x=-1/3 không là nghiệm của f(x)
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1 had gone away, I arrived at the party
2 reached the ground, the football match had ended
3 got to the airport, the plane had taken off
4 had done all the exercises, he went out with his friends
5 I arrived, Jack had left the office
6 he had done all his work, he went home
7 picked up their bags, they had eaten all the food
8 of 20, Madonna had become famous
9 I had heard the condition, I decided not to enter for the competition
10 Steven bought a new motorbike, he had saved enough money
1 A
2 A
3 A
4 A
![](https://rs.olm.vn/images/avt/0.png?1311)
R=1/2CD=a
h=AD=2a
S1=Sxq=2*pi*r*h=2*pi*a*2a=4*pi*a^2
S2=Stp=2*pi*r^2+2*pi*r*h
=2*pi*a^2+2*pi*a*2a
=6*pi*a^2
>S1/S2=2/3
![](https://rs.olm.vn/images/avt/0.png?1311)
Gọi hai số cần tìm lần lượt là a,a+1
Theo đề, ta co: a^2+(a+1)^2=85
=>2a^2+2a+1-85=0
=>a^2+a-42=0
=>a=6
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a: AC=12cm
Xét ΔABC có AB<AC<BC
nên \(\widehat{C}< \widehat{B}< \widehat{A}\)
b: Xét ΔABC vuông tại A và ΔAEC vuông tại A có
AB=AE
AC chung
Do đó: ΔABC=ΔAEC
c: Xét ΔCEB có
CA là đường trung tuyến
BH là đường trung tuyến
CA cắt BH tại M
Do đó: M là trọng tâm của ΔCEB
\(\overline{abcd}+\overline{abc}+\overline{ab}+a=8813\)
\(\Leftrightarrow1000a+100b+10c+d+\left(100a+10b+c\right)+\left(10a+b\right)+a=8813\)
\(\Leftrightarrow1111a+111b+11c+d=8813\)
- Nếu \(a\ge8\Rightarrow1111a\ge8888>8813\) (ktm)
- Nếu \(a\le6\Rightarrow1111a+111b+11c+d< 6666+999+99+9=7773< 8813\) (ktm)
\(\Rightarrow a=7\)
\(\Rightarrow7777+111b+11c+d=8813\)
\(\Rightarrow111b+11c+d=1036\)
- Nếu \(b\le8\Rightarrow111b+11c+d\le888+99+9=996< 1036\) (ktm)
\(\Rightarrow b>8\Rightarrow b=9\)
\(\Rightarrow999+11c+d=1036\Rightarrow11c+d=37\)
\(\Rightarrow11c=37-d\Rightarrow37-d\) chia hết cho 11 (1)
Mà \(0\le d\le9\Rightarrow28\le37-d\le37\) (2)
(1);(2) \(\Rightarrow37-d=33\Rightarrow d=4\)
\(\Rightarrow11c=33\Rightarrow c=3\)
Vậy \(\overline{abcd}=7934\)