（2+1）X*｛24.6*2÷[（2+1）X]｝÷2=24.63X*｛49.2÷[3X]｝=24.6×249.2=49.2这是恒等式所以只要满足除数不等于0所以x≠0
原式=[(x^2-4-12)/(x-2)]÷[-(x-4)/(x-2)]=[(x+4)(x-4)/(x-2)]×[-(x-2)/(x-4)]=-(x+4)(x-4)(x-2)/[(x-2)(x-4)]=-(x+4)=-√2
