已知三条直线l1:2x-y+a=0(a>0)直线l2:-4x+2y+1=0直线l3:x+y-1=0,且l1与l2间距离是7/10倍根号5.a=3,或a=-4

3）设点P(x,y),x>0;y>0,则 2,d(P,L1)=1/2*d(P,L2) --->|2x-y+3|=1/2*|-2x+y+1/2|; (|...-4|=1/2*|...|) --->2x-y+13/6=0 (-17/6).(1) 3,d(P,L1)/d(P,L3)=√2/√5 --->|2x-y+3 (-4)|/√5:|x+y+1|/√2=√2:√5 --->|2x...