giúp mk bài 2 với ạ 
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Những câu hỏi liên quan
29 tháng 8 2021
Bài 18:
a: Ta có: \(P=\left(\dfrac{\sqrt{a}}{2}-\dfrac{1}{2\sqrt{a}}\right)^2\cdot\left(\dfrac{\sqrt{a}-1}{\sqrt{a}+1}-\dfrac{\sqrt{a}+1}{\sqrt{a}-1}\right)\)
\(=\dfrac{\left(\sqrt{a}-1\right)^2\cdot\left(\sqrt{a}+1\right)^2}{4a}\cdot\dfrac{a-2\sqrt{a}+1-a-2\sqrt{a}-1}{\left(\sqrt{a}+1\right)\left(\sqrt{a}-1\right)}\)
\(=\dfrac{\left(a-1\right)\cdot\left(-4\right)\cdot\sqrt{a}}{4a}\)
\(=\dfrac{-a+1}{\sqrt{a}}\)
b: Để P<0 thì -a+1<0
\(\Leftrightarrow-a< -1\)
hay a>1
c: Để P=-2 thì \(-a+1=-2\sqrt{a}\)
\(\Leftrightarrow-a+1+2\sqrt{a}=0\)
\(\Leftrightarrow a-2\sqrt{a}+1=2\)
\(\Leftrightarrow\left(\sqrt{a}-1\right)^2=2\)
\(\Leftrightarrow\sqrt{a}-1=\sqrt{2}\)
hay \(a=3+2\sqrt{2}\)
29 tháng 8 2021
Bài 17:
a: Ta có: \(P=\dfrac{a\sqrt{a}-1}{a-\sqrt{a}}-\dfrac{a\sqrt{a}+1}{a+\sqrt{a}}+\left(\sqrt{a}-\dfrac{1}{\sqrt{a}}\right)\left(\dfrac{\sqrt{a}+1}{\sqrt{a}-1}+\dfrac{\sqrt{a}-1}{\sqrt{a}+1}\right)\)
\(=\dfrac{a+\sqrt{a}+1-a+\sqrt{a}-1}{\sqrt{a}}+\dfrac{a-1}{\sqrt{a}}\cdot\dfrac{a+2\sqrt{a}+1+a-2\sqrt{a}+1}{a-1}\)
\(=2+\dfrac{2a+2}{\sqrt{a}}\)
\(=\dfrac{2a+2\sqrt{a}+2}{\sqrt{a}}\)
27 tháng 12 2021
Bài 1:
Gọi số cây 3 lớp 7A,7B,7C lần lượt là \(a,b,c\in \mathbb{N^*},cây\)
Áp dụng tc dtsbn:
\(\dfrac{a}{6}=\dfrac{b}{4}=\dfrac{c}{5}=\dfrac{a+b+c}{6+4+5}=\dfrac{30}{15}=2\\ \Rightarrow\left\{{}\begin{matrix}a=12\\b=8\\c=10\end{matrix}\right.\)
Vậy ...
Bài 3:
\(a+b\ne-c\Rightarrow a+b+c\ne0\\ \Rightarrow\dfrac{a+b-c}{c}=\dfrac{b+c-a}{a}=\dfrac{c+a-b}{b}=\dfrac{a+b+c}{a+b+c}=1\\ \Rightarrow\left\{{}\begin{matrix}a+b-c=c\\b+c-a=a\\c+a-b=b\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}a+b=2c\\b+c=2a\\c+a=2b\end{matrix}\right.\\ \Rightarrow P=\dfrac{a+b}{a}\cdot\dfrac{a+c}{c}\cdot\dfrac{b+c}{b}=\dfrac{2a\cdot2b\cdot2c}{abc}=8\)
TL
1
29 tháng 8 2021
Bài 13:
a: Ta có: \(P=\dfrac{15\sqrt{x}-11}{x+2\sqrt{x}-3}+\dfrac{3\sqrt{x}-2}{1-\sqrt{x}}-\dfrac{2\sqrt{x}+3}{\sqrt{x}+3}\)
\(=\dfrac{15\sqrt{x}-11-\left(3\sqrt{x}-2\right)\left(\sqrt{x}+3\right)-\left(2\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{15\sqrt{x}-11-3x-9\sqrt{x}+2\sqrt{x}+6-2x+2\sqrt{x}-3\sqrt{x}+3}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{-5x+7\sqrt{x}-2}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{-5\sqrt{x}+2}{\sqrt{x}+3}\)
b: Để \(P=\dfrac{1}{2}\) thì \(-10\sqrt{x}+4=\sqrt{x}+3\)
\(\Leftrightarrow-11\sqrt{x}=-1\)
hay \(x=\dfrac{1}{121}\)
MN
giúp mk câu c
bài 2 tự luận câu c bài hình vs 2 bài cuối với ạ
1
DT
Đỗ Thanh Hải
CTVVIP
11 tháng 6 2021
1 Because she went to bed late last night, she couldn't go to school on time
2 It rained heavily so we couldn't go to the theater
3 The wind was strong, so the tree in my garden was uprooted
4 He fell asleep while driving, so he had an accident
5 If I had a guitar here, I could sing you a song
6 If I didn't need to finish my assignment, I could help you with your homework
7 If you don't study hard, you may fail the exam
8 If there is no oil in the engine, the car will breakdown
9 If it hadn't been for your help, I couldn't have finished the report
10 If it hadn't been for her disapprova, he would have been given that job
11 The house seemed as if it had been occupied for years
Diện tích mảnh vườn là
15x15=225(m2)
Trên cả mảnh vườn thu hoạch đc số kg cà chua là
10x(225:1)=2250(kg)