In the graph shown, at what value of x does the value of y change from increasing to decreasing or decreasing to increasing?
1 answer:
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Not sure why such an old question is showing up on my feed...
Anyway, let
and 
. Then we want to find the exact value of 
.
Use the angle difference identity:
and right away we find
. By the Pythagorean theorem, we also find 
. (Actually, this could potentially be negative, but let's assume all angles are in the first quadrant for convenience.)
Meanwhile, if
, then (by Pythagorean theorem) 
, so 
. And from this, 
.
So,
Anyway, let
Use the angle difference identity:
and right away we find
Meanwhile, if
So,