How are you? I hope you are doing well at university these days. You haven't written to me about your examinations but I believe that you passed your exam easy.

        Anyway, on December  30th 2021 will be my birthday. To celebrate my 35th birthday, I am going to hold a warm dinner at Manh Hoach restaurant near Luc Quan crossroad, Co Dong, Son Tay, Ha Noi at 6.00 in the evening of the 2nd next Sunday. I am going to invite all of my friends. I will be very eager to meet you in there

            The dinner will start at 6 o clock, but you can come more earlier and we can go fishing at the lake. Bring your wife along with you too. Don't be late.

        I hope you would accept my invitation.

       Your sincerely,

                 Tham khảo ạ!

Gọi độ dài cạnh là a

Diện tích hình vuông là S=a^2

Độ dài bán kính hình tròn là a/2

Diện tích hình tròn là: (a/2)^2*3,14=a^2*3,14/4

Theo đề, ta có: a^2-a^2*3,14/4=0,215

=>a^2=1

=>a=1

=>Diện tích hình tròn là: 1^2*3,14/4=0,785cm²

\(2H_2+O_2\rightarrow2H_2O\)

\(4Mg+O_2\rightarrow2Mg_2O\)

\(2Cu+O_2\rightarrow2CuO\)

\(2S+O_2\rightarrow2SO\)

\(4Al+3O_2\rightarrow2Al_2O_3\)

\(2C+O_2\rightarrow2CO\)

\(a,\left(-8,5\right)+16,35+\left(-4,5\right)-\left(-2,25\right)\\ =\left[\left(-8,5\right)+\left(-4,5\right)\right]+\left[16,35-\left(-2,25\right)\right]\\ =-13+18,6=5,6\\ b,5,63+\left(-2,75\right)-\left(-8,94\right)+9,06-15,25\\ =5,63-2,75+8,94+9,06-15,25\)

\(=5,63-\left(2,75+15,25\right)+\left(8,94+9,06\right)\\ =5,63-18+18\\ =5,63\)

a) (-8,5) + 16,35 + (-4,5) - (-2,25) = 5,6       

b)  5,63 + (-2,75) - (-8,94) + 9,06 - 15,25 = 5,63

\(P=\dfrac{18}{x}+\dfrac{9}{y}+\dfrac{x}{6}-\dfrac{5y}{12}+2019\)

\(P=\left(\dfrac{x}{2}+\dfrac{18}{x}\right)+\left(\dfrac{y}{4}+\dfrac{9}{y}\right)-\dfrac{1}{3}\left(x+2y\right)+2019\)

\(P\ge2\sqrt{\dfrac{18x}{2x}}+2\sqrt{\dfrac{9y}{4y}}-\dfrac{1}{3}.18+2019=2022\)

Dấu "=" xảy ra khi \(x=y=6\)

em cảm ơn thầy ạ 

\(P=\frac{a^3}{\left(a-b\right)\left(a-c\right)}+\frac{b^3}{\left(b-a\right)\left(b-c\right)}+\frac{c^3}{\left(c-a\right)\left(c-b\right)}\)

\(=\frac{a^3}{\left(a-b\right)\left(a-c\right)}-\frac{b^3}{\left(a-b\right)\left(b-c\right)}+\frac{c^3}{\left(a-c\right)\left(b-c\right)}\)

\(=\frac{a^3\left(b-c\right)-b^3\left(a-c\right)+c^3\left(a-b\right)}{\left(a-b\right)\left(a-c\right)\left(b-c\right)}\)

\(=\frac{a^3b-a^3c-ab^3+cb^3+c^3\left(a-b\right)}{\left(a-b\right)\left(a-c\right)\left(b-c\right)}\)

\(=\frac{-c\left(a^3-b^3\right)+ab\left(a^2-b^2\right)+c^3\left(a-b\right)}{\left(a-b\right)\left(a-c\right)\left(b-c\right)}\)

\(=\frac{-c\left(a-b\right)\left(a^2+ab+b^2\right)+ab\left(a-b\right)\left(a+b\right)+c^3\left(a-b\right)}{\left(a-b\right)\left(a-c\right)\left(b-c\right)}\)

\(=\frac{-c\left(a^2+ab+b^2\right)+ab\left(a+b\right)+c^3}{\left(a-c\right)\cdot\left(b-c\right)}=\frac{-a^2c-abc-b^2c+a^2b+ab^2+c^3}{\left(a-c\right)\left(b-c\right)}\)

\(=\frac{c\left(c^2-a^2\right)+b^2\left(a-c\right)+ab\left(a-c\right)}{\left(a-c\right)\left(b-c\right)}=\frac{c\left(c-a\right)\left(c+a\right)_{}+\left(a-c\right)\left(b^2+ab\right)}{\left(a-c\right)\left(b-c\right)}\)

\(=\frac{-c\left(c+a\right)+b^2+ab}{b-c}=\frac{b^2+ab-c^2-ac}{b-c}=\frac{\left(b-c\right)\left(b+c\right)+a\left(b-c\right)}{b-c}\)

=b+c+a

góc ACK = 90⁰- góc KAC=90⁰-55⁰=35⁰
góc M2=90⁰-góc ACK=90⁰-35⁰=55 độ
góc BMC = 180 độ - góc M2=180⁰-55⁰=125 độ

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