Question

find exact value of tan -1(1)

Answer 1

well think about the inverse of arctan
which is tan. now that angle measure make tan 1

Answer 2

tan(?)=1

Answer 3

for that we look at this special triangle that has two side 1
and two angles 45
we know that tan=adjacent/hypotenuse
tan(45)=1/1=1
so the angle is 45 degrees
now going back the what we said arctan is inverse of tan
so if we have tan(45)=1===> 45=arctan(1)
mean that arctan(1)=45 (pi/4 is radians)