The correct option is B √(a2b2+b2c2+c2a2)2
Let A(a,0,0),B(0,b,0) and C(0,0,c
Then −−→AB=B−A=(0,b,0)−(a,0,0)=(−a,b,0)
And −−→AC=C−A=(0,0,c)−(a,0,0)=(−a,0,c)
Now −−→AB×−−→AC=∣∣
∣∣ijk−ab0−a0c∣∣
∣∣=i(bc−0)−j(−ac−0)+k(0+ab)=bci+acj+abk
Therefore area of ΔABC=∣∣∣−−→AB×−−→AC∣∣∣2=√(bc)2+(ac)2+(ab)22