We'll choose a function whose domain of definition is (0 ;
3pi/180).
The function is f(x) = (tan
x)/x
We'll do the first derivative test to verify the if
the function is monotonic. We'll apply the quotient
rule:
f'(x) = [(tan x)'*x - (tan
x)*(x)']/x^2
f'(x) = [x/(cos x)^2 - sin x/cos
x]/x^2
f'(x) = (x - sin x*cos x)/x^2*(cos
x)^2
We notice that the numerator is positive for any value
from the domain of definition and the denominator is always
positive.
Then f'(x)>0 => the function is
monotonically increasing.
If so, for x=2pi/180 <
x=3pi/180 => f(2pi/180) < f(3pi/180)
But
f(2pi/180) = tan (2pi/180)/(2pi/180)
f(3pi/180) = tan
(3pi/180)/(3pi/180)
tan (2pi/180)/(2pi/180) < tan
(3pi/180)/(3pi/180)
We'll simplify by
pi/180:
(tan 2)/2 < (tan
3)/3
We'll cross multiply and we'll
get:
3*tan 2 < 2*tan
3
Comparing the given values, we have found
the inequality: 3*tan 2 < 2*tan 3.
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