Question 550103
modulus (||symbol) value should not negative
the condition is a<b
we know that |x|= plus or minus x
so |a-b|=a-b or -(a-b)
but here if we take |a-b|=a-b = -ve value(from the above condition) 
so here we have to  take |a-b|=-(a-b) which gives positive value