Let f(x) be a cubic polynomial on R which increases in the interval (-[infinity],0)∪(1,[infinity]) and decreases in the interval (0, 1). If f'(2)=6 and f(2)=2 , then the value of tan−¹ (f(1)) + tan−¹ (f(3/2)) + tan−¹ (f(0)) equals: