The correct option is C a−b+c>0
ax+by+c=0 ⋯(1)
bx+ay+c=0 ⋯(2)
(1)×a−(2)×b, we get
x=−ca+b
Since, the two lines are symmetric about the line y=x, the intersection point lies on the line y=x.
∴y=−ca+b
Or, substitute the value of x in eqn (1), we get y=−ca+b
Now, √(1+ca+b)2+(1+ca+b)2<2√2
Squaring both the sides (as terms are positve)
⇒2(a+b+ca+b)2<8
⇒(a+b+ca+b)2<4
⇒−2<(a+b+ca+b)<2
⇒−2a−2b<a+b+c<2a+2b
⇒−2a−2b<a+b+c or a+b+c<2a+2b
⇒−3a−3b−c<0 or −a−b+c<0
⇒3a+3b+c>0 or a+b−c>0
Since, a+b−c>0 and a>b
∴a−b+c>0
Hence, both a+b−c>0 and a−b+c>0 are correct.
Alternate solution:
∵a>b>c>0
⇒a−b>0 and a−c>0
⇒a−b+c>0 and a+b−c>0