已知2a²＋a－4＝0,a－b＝2,求1/a+1+2/b的值

已知2a²＋a－4＝0,a－b＝2,求1/a+1+2/b的值

｛2a²＋a－4＝0,①
｛a－b＝2,②
①==>(a²+a)+(a²-4)=0
==> a(a+1)+(a-2)(a+2)=0 ③
②==> a=b+2 ,a-2=b代入 ③
==> (b+2)(a+1)+b[(a+1)+1]]=0
==>2b(a+1)+2(a+1)+b=0
==>2(a+2)+b=- 2b(a+1)
==> [b+2(a+1)]/[(a+1)b]=-2
∴1/(a+1)+2/b
=(b+2(a+1)/[(a+1)b]
=-2

0是0就是0一定是0的