由√2≈1.4142，√20=2√5≈4.472，√0.2-√200=√2/10-√20×20÷2=√4/20-√20×20÷2=2÷4.472-4.472²÷1.414=0.477-14.143=-13.67.
根号0.2-根号200=(根号20)/10-10根号2≈-13.69
