Đáp án: 

3c

4d

5a

6c

7b

8b

9a

10d

Vote cho mik vs nha.

3.

Gọi 2 cạnh của hcn là ab \(\Rightarrow\) nửa chu vi \(a+b=\dfrac{20}{2}=10\)

Áp dụng BĐT cô-si: \(a+b\ge2\sqrt{ab}\Rightarrow ab\le\left(\dfrac{a+b}{2}\right)^2=25\)

Vậy B đúng

4.

\(-2x^2\ge5x\Leftrightarrow5x+2x^2\le0\)

D đúng

3

a) S

b)Đ

c)Đ

d)S

Bài 3.

Công vật thực hiện:

\(A=Fs\cdot cos\alpha=150\cdot15\cdot cos45^o=1591J\)

Công suất vật thực hiện:

\(P=F\cdot v=150\cdot1,5=225W\)

Thấy : \(\widehat{PBQ}=\widehat{BQA}-\widehat{BPQ}=55^o-15^o=40^o\)

Ta có : \(\dfrac{PQ}{sin40^o}=\dfrac{BQ}{sin15^o}\Rightarrow BQ=\dfrac{100}{sin40^o}.sin15^o\approx40,27\left(m\right)\)

\(\dfrac{BQ}{sin90^o}=\dfrac{AB}{sin55^o}\Rightarrow AB\approx40,27.sin55^o\approx33\left(m\right)\)

\(=\lim\limits_{x\rightarrow-1}\dfrac{\dfrac{x+2017-\left(2015-x\right)}{\sqrt[3]{\left(x+2017\right)^2}+\sqrt[3]{\left(x+2017\right)\left(2015-x\right)}+\sqrt[3]{\left(2015-x\right)^2}}}{\dfrac{2000+x-\left(1998-x\right)}{\sqrt{2000+x}+\sqrt{1998-x}}}\)

\(=\lim\limits_{x\rightarrow-1}\dfrac{\sqrt{2000+x}+\sqrt{1998-x}}{\sqrt[3]{\left(x+2017\right)^2}+\sqrt[3]{\left(x+2017\right)\left(2015-x\right)}+\sqrt[3]{\left(2015-x\right)^2}}\)

\(=\dfrac{\sqrt{1999}+\sqrt{1999}}{\sqrt[3]{2016^2}+\sqrt[3]{2016^2}+\sqrt[3]{2016^2}}=\dfrac{2\sqrt{1999}}{3.24\sqrt[3]{294}}=\dfrac{\sqrt{1999}}{36\sqrt[3]{294}}\)

\(\Rightarrow a+b=1999+294\)

22222 - 13345 = 9877

345678 + 456456 = 801134

987888 - 111111 + 2021 = 878798

1111111 - 234456 + 234 = 879032

đỏi số 4 ^ 56 thành 4 ^ 4 nhé

Đs: 5192296858534827628552786197008883