换底公式lg(4-x)/lg2-lg(x-1)/lg4=1lg(4-x)/lg2-lg(x-1)/2lg2=1两边乘2lg22lg(4-x)-lg(x-1)=2lg2lg(4-x)²-lg(x-1)=2lg2lg[(4-x)²/(x-1)]=lg2²(4-x)²/(x-1)=4x²-8x+16=4x-4x²-12x+20=0...