2. a) \(x^2-6x+9\)

\(=\left(x-3\right)^2\)

b) \(x^2+x+\dfrac{1}{4}\)

= \(x^2+2x\dfrac{1}{2}+\dfrac{1}{4}\)

\(=\left(x+\dfrac{1}{2}\right)^2\)

c) \(2xy+x^2y^2+1\) ( mình nghĩ là 2xy thôi nên sửa lại nhé :v )

= \(\left(xy+1\right)^2\)

3. \(x^2-y^2=\left(x-y\right)\left(x+y\right)\)

Thế x = 87; y = 13 ta có: \(\left(87-13\right)\left(87+13\right)=7400\)

Bài 1:

a) \(6\left(x+1\right)^2-\left(x-3\right)\left(x^2+3x+9\right)+\left(x-2\right)^2\)

\(\Leftrightarrow6x^2+12x+6-x^3+27+x^2-4x+4\)

\(\Leftrightarrow-x^3+7x^2+8x+37\)

với x = 2 ta có \(\left(-2\right)^3+7.2^2+8.2+37=73\)

b) ( 2x - 1)(3x + 1) + ( 3x - 4)(3 - 2x)

\(\Leftrightarrow6x^2+2x-3x-1+9x-6x^2-12+8x\)

\(\Leftrightarrow16x-13\)

Với x = \(\dfrac{9}{8}\) ta có: \(16.\dfrac{9}{8}-13=5\)

lan is our classmate.she comes....from..Nha Trang.she is..in.class 7a.she is 30 years old.her parents ..live.in Nha Trang.now she's living.with..her aunt and uncle in HCM city.her house is ..far..from school.so, she usually goes to school by.bus.sometimes,her aunt takes her to school by..motorbike.she doesn't have ..any.friends.so she feels sad

\(n_{NaOH}=0,5.0,02=0,01\left(mol\right)\)

\(n_{HCl}=1.0,3=0,3\left(mol\right)\)

\(Pt:NaOH+HCl\rightarrow NaCl+H_2O\)

0,01 mol 0,3mol\(\rightarrow0,01mol\)

Lập tỉ số: n_NaOH : n_HCl = 0,01 < 0,3

\(\Rightarrow\) NaOH hết; HCl dư

\(m_{NaCl}=0,01.58,5=0,585\left(g\right)\)

\(n_{HCl\left(dư\right)}=0,3-0,01=0,29\left(mol\right)\)

\(C_{M_{HCl\left(Dư\right)}}=\dfrac{0,29}{0,3}=1M\)