You need to construct at least 2 angle bisectors to help locate the incircle's center (aka the "incenter"). The incircle is the largest circle possible that is inside the triangle, that doesn't overflow or spill outside of the triangle. An angle bisector cuts an angle in half.
Answer:
Part a)
Part b) 
Part c) (s+t) lie on Quadrant IV
Step-by-step explanation:
[Part a) Find sin(s+t)
we know that

step 1
Find sin(s)

we have

substitute




---> is positive because s lie on II Quadrant
step 2
Find cos(t)

we have

substitute




is negative because t lie on II Quadrant
step 3
Find sin(s+t)

we have



substitute the values



Part b) Find tan(s+t)
we know that
tex]tan(s + t) = (tan(s) + tan(t))/(1 - tan(s)tan(t))[/tex]
we have



step 1
Find tan(s)

substitute

step 2
Find tan(t)

substitute

step 3
Find tan(s+t)

substitute the values




Part c) Quadrant of s+t
we know that
----> (s+t) could be in III or IV quadrant
----> (s+t) could be in III or IV quadrant
Find the value of cos(s+t)

we have



substitute



we have that
-----> (s+t) could be in I or IV quadrant
----> (s+t) could be in III or IV quadrant
----> (s+t) could be in III or IV quadrant
therefore
(s+t) lie on Quadrant IV
Answer:
Step-by-step explanation:
Perpendicular to y=-3
perpendicular means meeting at a right angle so the line youre looking for will be x=?
it passes through (-8,-3) so the equation of the line is simply x=-8