Áp dụng BĐT Bun-hia-cop-xki ta có:

\(\left(a^2+b^2+c^2\right)\left(1+1+1\right)\ge\left(a+b+c\right)^2\)

\(\Leftrightarrow a^2+b^2+c^2\ge\frac{\frac{9}{4}}{3}=\frac{3}{4}\left(đpcm\right)\)

Dấu '=' xảy ra khi \(\hept{\begin{cases}a=b=c\\a+b+c=\frac{3}{2}\end{cases}\Leftrightarrow a=b=c=\frac{1}{2}}\)

\(2,5\times9,2\times50\times0,4\)

\(=\left(2,5\times0,4\right)\times\left(9,2\times50\right)\)

\(=1\times460\)

\(=460\)

2,5 x 9,2 x 50 x 0,4

= ( 2,5 x 0,4 ) x ( 9,2 x 50 )

= 1 x 460

= 460

Study well ! >_<

1: -> Linh and her (his, my, our, their,...) parents are proud of him because he always gets good marks.

2: -> We are very interested in playing soccer when we live in the countryside.

3: -> I haven't talked to uncle since he bought a new house in the city center.

4: -> The Browns will buy a lot of food because they are going to have a party.

5: -> It only a small car so there're not enough room for all of us.

1. Linh's parents are very proud of him because he always gets good marks.

2. We were very interested in playing soccer when we lived in the countryside.

3. I haven't talked to my uncle since he bought a new house in the city center.

4. The Browns have bought a lot of food because they are going to have a party.

5. It is only a small car, so there is not enough room for all of us

a. P(x)+Q(x)=(x³-3x-x²+1)+(2x²-x³+x-5)

                  =( x³-x³) +(-x²+2x²)+(-3x+x)+(1-5)

                  =    x²-2x-4         

    P(x)-Q(x)=(x³-3x-x²+1)-(2x²-x³+x-5)

                   = x^3_3x-x²+1-2x²+x³+x+5

                  = ( x³+x³) +(-x^2_2x²)+(-3x-x)+(1+5)

                  =  2x^3_3x²-4x+6