Answer:
0 < a < 6
or
(0, 6) in interval notation
Explanation:
The area of the triangle is

We are given base = 6 in, height = a and area A < 18 in²
Using the formula for area we get

We know this area is < 18
So 3a < 18
Dividing both sides by 3 gives us
3a/3 < 18/3
a < 6
So height a must be less than 6 inches.
Height cannot be 0 so the lower bound on height is
a > 0
Putting these together we get the rang of a as
0 < a < 6
In Interval notation this is written as (0, 6)
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