Công thức phân tử C₆H₁₂O₆

 Câu1. a/b = 36/45 = 4/5 
suy ra ƯCLN = a/4. 
Mà BCNN = ab/ƯCLN 
suy ra 300 = ab/(a/4) 
suy ra b = 75 
suy ra a = 60 

a) \(\left(a+b\right)\left(a^2-ab+b^2\right)+\left(a-b\right)\left(a^2+ab+b^2\right)\)

\(=a^3+b^3+a^3-b^3=2a^3\)

Vậy \(\left(a+b\right)\left(a^2-ab+b^2\right)+\left(a-b\right)\left(a^2+ab+b^2\right)=2a^3\)

4P + 5O₂\(\rightarrow\)2P₂O₅

4........5...........2 (mol)

0,2 (mol)

nP= \(\dfrac{m}{M}=\dfrac{6,2}{31}=0,2\left(mol\right)\)

nO₂=\(\dfrac{0,2.5}{4}=0,25\left(mol\right)\)

VO₂=n.22,4=0,25.22,4=5,6(l)

nP₂O₅=\(\dfrac{0,2.2}{4}=0,1\left(mol\right)\)

mP₂O₅=n.M=0,1.142=14,2(g)

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

\(\Leftrightarrow x^2-4-x^2-\left(x^2+x-3x-3\right)\)

\(\Leftrightarrow x^2-4-x^2-x+3x+3\)

\(\Leftrightarrow2x-1\)

b) \(\left(2x+1\right)^2+\left(3x-1\right)^2+2\left(2x+1\right)\left(3x-1\right)\)

\(\Leftrightarrow\left[\left(2x+1\right)+\left(3x-1\right)\right]^2\)

\(\Leftrightarrow\left(2x+1+3x-1\right)^2=\left(5x\right)^2=25x^2\)

8/ 2NaOH + H₂SO₄\(\rightarrow\)Na₂SO₄+2H₂O

15/ N₂O₅+H₂O\(\rightarrow\)2HNO₃

17/ Al₂O₃+3H₂SO₄\(\rightarrow\)Al₂(SO₄)₃+3H₂O

\(A=x^2+10x+29\)

\(=x^2+2.x.5+5^2+4\)

\(=\left(x+5\right)^2+4\)

Ta có: \(\left(x+5\right)^2\ge0\forall x\)

\(\Rightarrow\left(x+5\right)^2+4\ge4>0\)

\(\Rightarrow\left(x+5\right)^2+4>0\)

Vậy A>0