\(=7^2-2.7.3x+\left(3x\right)^2\)

\(=49-42x+9x^2\)

\(\left(7-3x\right)^2\)

\(=7^2-2.7.3x+\left(3x\right)^2\)

\(=49-42x+9x^2\)

Hoàn thiện HĐT ta thu được các đơn thức cần điền vào “…”.

a)  x 2 + 4x + 4 = ( x   +   2 ) 2 .           b) 4 x 2 – 12x + 9 = ( 2 x   –   3 ) 2 .

c) 4 x 2  – 12xy + 9 y 2 = ( 2 x   –   3 y ) 2 .

Chú ý: phép trừ ta chuyển thành cộng đại số.

d)  x − y 2 x + y 2 = x 2 − y 2 4 .

\(\left(1\right)CuO+2HCl\rightarrow CuCl_2+H_2O\\ \left(2\right)CuCl_2+2KOH\rightarrow Cu\left(OH\right)_2\downarrow+KCl\\ \left(3\right)Cu\left(OH\right)_2+H_2SO_4\rightarrow CuSO_4+2H_2O\\ \left(4\right)CuSO_4+BaCl_2\rightarrow CuCl_2+BaSO_4\downarrow\)

\(1.Cu\left(OH\right)_2\text{ }\left(M\right)\underrightarrow{^{^{t^0}}}CuO\left(A_1\right)+H_2O\left(B_1\right)\)

\(2.CuO+2HCl\left(D_1\right)\rightarrow CuCl_2\left(A_2\right)+H_2O\)

\(3.CuCl_2+2AgNO_3\left(D_2\right)\rightarrow Cu\left(NO_3\right)_2\left(A_3\right)+2AgCl\)

\(4.Cu\left(NO_3\right)_2+2NaOH\rightarrow Cu\left(OH\right)_2+2NaNO_3\)

\(5.H_2O+SO_3\left(E_1\right)\rightarrow H_2SO_4\left(B_2\right)\)

\(6.H_2SO_4+CuCO_3\left(E_2\right)\rightarrow CuSO_4\left(B_3\right)+CO_2+H_2O\)

\(7.CuSO_4+2KOH\left(E_3\right)\rightarrow Cu\left(OH\right)_2+K_2SO_4\)

a, (1) 2Ca + O2 -> (t°) 2CaO

(2) CaO + H2O -> Ca(OH)2 

(3) 2H2 + O2 -> (t°) 2H2O

(4) P2O5 + 3H2O -> 2H3PO4

b, (1) Zn + 2HCl -> ZnCl2 + H2O

(2) 2H2 + O2 -> (t°) 2H2O

(3) BaO + H2O -> Ba(OH)2

(4) ZnO + H2 -> (t°) Zn + H2O

c, (1) 4P + 5O2 -> (t°) 2P2O5

(2) P2O5 + 3H2O -> 2H3PI4

(3) 2Na + H3PO4 → Na2HPO4 + H2

(4) HgO + H2 -> (t°) Hg + H2O

1/ (1) O2 + 2Ca -t--> CaO 
(2) CaO + H2O ---> Ca(OH ) 2 
(3) O2 + 2H2 ----> 2H2O
(4) 3H2O + P2O5 ---> 2H3PO4
2/ (1) 6HCl + Al ---> AlCl3 +3H2
  (2) 2H2 +O2 --> H2O 
 (3) H2O + BaO ---> Ba(OH) 2

\(2Cu+O_2\underrightarrow{^{^{t^0}}}2CuO\)

\(CuO+2HCl\rightarrow CuCl_2+H_2O\)

\(CuCl_2+2NaOH\rightarrow Cu\left(OH\right)_2+2NaCl\)

\(CuCl_2+2AgNO_3\rightarrow Cu\left(NO_3\right)_2+2AgCl\)

a, (1) \(4Na+O_2\underrightarrow{t^o}2Na_2O\)

(2) \(Na_2O+H_2O\rightarrow2NaOH\)

(3) \(2NaOH+H_2SO_4\rightarrow Na_2SO_4+2H_2O\)

(4) \(Na_2SO_4+BaCl_2\rightarrow BaSO_{4\downarrow}+2NaCl\)

b, (1) \(2KMnO_4\underrightarrow{t^o}K_2MnO_4+MnO_2+O_2\)

(2) \(Ca+\dfrac{1}{2}O_2\underrightarrow{t^o}CaO\)

(3) \(CaO+H_2O\rightarrow Ca\left(OH\right)_2\)

(4) \(Ca\left(OH\right)_2+CO_2\rightarrow CaCO_{3\downarrow}+H_2O\)

\(9x^2-12xy+4y^2=\left(3x-2y\right)^2\)

\(9x^2-12xy+4y^2=\left(3x-2y\right)^2\)