根号12-根号（3/4）=2根号3-1/2*根号3=3/2*根号3
√12=2√3√(3/4)=√3/2所以结果为3√3/2
2根号3减二分之一根号3等于二分之三根号3
=2倍根号3-1/2根号3=（3/2）根号3
