hu..hu ai do giup minh lam bai di 

Cần ít nhất bao nhiêu gam Al để khử hoàn toàn 6,96 gam Fe₃O₄ (Biết phản ứng xảy ra hoàn toàn).

A. 1,62.

B. 2,70.

C. 2,16.

D. 3,24.

a,b.ab,a=ab,ab

=>ab.aba=abab

=>ab.aba=ab.101

=>aba=101

=>(a;b)=(1;0)

vậy (a;b)=(1;0)

\(a,x^2-5=x^2-\left(\sqrt{5}\right)^2=\left(x-\sqrt{5}\right)\left(x+\sqrt{5}\right)\)

\(b,x^4+x^3+x+1=x^3.\left(x+1\right)+\left(x+1\right)\)

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

\(=\left(x+1\right)^2\left(x^2-x+1\right)\)

\(c,x^3-19x-30=x^3-25x+6x-30\)

\(=x.\left(x^2-25\right)+6.\left(x-5\right)\)

\(=x.\left(x-5\right)\left(x+5\right)+6.\left(x-5\right)\)

\(=\left(x-5\right).\left[x\left(x+5\right)+6\right]\)

\(=\left(x-5\right).\left(x^2+5x+6\right)\)

\(=\left(x-5\right).\left(x^2+2x+3x+6\right)\)

\(=\left(x-5\right)\left[x.\left(x+2\right)+3.\left(x+2\right)\right]\)

\(=\left(x-5\right)\left(x+2\right)\left(x+3\right)\)

\(\frac{x}{5}\)-\(\frac{5}{2}\)=-31