if the straight line 2x+3y=1, x+ 2y=1 and ax + by =1 form a triangle with origin as orthocenter , then (a,b) is

solving first two lines you get the point opposite to the side formed by ax+by-1=0 .the point i s P1(-1,1).

since the origin is the orthocentre the product of slope joining P1 and oigin should be perpendicular to the variable line.

from the above condition u get the condition that a= -b .

using second and third line ,the line passing throught the point on intersection and origin is x(a-1)+y(b-2)=0 .this line is perpendicular to the first  line. this gives you the second condition u need to get values of a and b