已知a=-(√ 2 1)，b=√ 2-1，求a^3b ab^3的值

千问 · 2012-2-21 01:24:54

a=-(√21)，b=√2-1=-√2-1ab=1-2=-1a=32√2b=3-2√2ab=6a^3bab^3=ab(ab)=(-1)x6=-6

千问 · 2012-2-21 01:24:54

a^3bab^3=ab﹙a＋b﹚=ab[﹙a＋b﹚－2ab]=﹙-1-√2﹚×﹙√2-1)×[﹙-1-√2＋√2-1)－2×﹙-1-√2﹚×﹙√2-1)]=﹙1-2)×[﹙-2﹚－2×﹙1-2﹚]=－1×﹙4＋2﹚=－6赞同

千问 · 2012-2-21 01:24:54

a^3bab^3=ab(a^2b^2)=ab[(a^22abb^2)-2ab]=ab[(ab)^2-2ab]=-(√21)(√2-1){[-(√21)(√2-1)]^2-2*[-(√21)(√2-1)]}=-(√21)(√2-1){[-√2-1√2-1]^2-2*[-(√21)(√2-1)]}=-{(-2)^2-2*(-1)}=-{42}=-6赞同