求证:直线l (m+2)x-(1+m)y-(6+4m)=0与点P(4,-1)的距离不等于3
问题描述:
求证:直线l (m+2)x-(1+m)y-(6+4m)=0与点P(4,-1)的距离不等于3
答
点(4,-1)到直线距离d=|4m+8+1+m-6-4m|/√(m+2)²+(1+m)²=|m+3|/√(m+2)²+(1+m)²反证法假设d=3那么|m+3|/√(m+2)²+(1+m)²=3m²+6m+9=9(m²+4m+4+m²+2m+1)化简17m&...