令t=lgx,则方程2lg²x-lgx4 + 1=0变形为2t²-4t + 1=0即t²-2t + 1/2=0
设t1=lga,t2=lgb,则t1+t2=lga+lgb=lg（ab）=2
lg（ab）×（logab+logba）=2×（2+2）=8