MHB Calculate the area of a triangle knowing its perimeter and 2 heights

AI Thread Summary
To calculate the area of a triangle with a perimeter of 30 m and heights of 8 m and 9 m, various methods can be utilized, including using the area formulas based on base and height, as well as Heron's formula. The area can be expressed in terms of the triangle's sides, leading to equations that relate the sides to the given perimeter. By substituting values and solving for one variable, potential solutions for the area were found, with the final calculations suggesting an area of approximately 42.93 m² or 36.28 m². Graphing the derived equations indicated three possible solutions for one side of the triangle, with two valid areas identified. The discussion emphasizes the importance of using both geometric and algebraic approaches to find the area.
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Calculate the area of a triangle knowing its perimeter and 2 heights

perimeter = 30 m
ha = 8 m
hb = 9 mNOTE = You can use the online triangle calculator TrianCal to see and draw the results.
NOTE = Do not use the values ??of responses.

A) 41.29 m2
B) 42.93 m2 or 36.28 m2
C) 42.95 m2 or 36.29 m2
D) Imposible
 
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Hello, here is what I did (this was the first idea that came to mind and it's kind of a brute force method):

Assuming the sides of the triangle are a,b,c, we have the following equations:

a+b+c+=30

The area of the triangle can be written in 3 different ways.

2 of them using A = Base * Height / 2

A = 8a/2

A = 9b/2

3rd one using Heron's Formula:

Semi-perimeter is 30/2 = 15 so

A = \sqrt{15(15-a)(15-b)(15-c)}

Now, to get an equation in only one unknown, let's pick a.

From equalizing the first 2 formulas for the area, we should get

b = 8a/9

From the perimeter, substituting b and solving for c we should get

c=(270-17a)/9

You should be able to get these answers fairly easy yourself.

Lastly, to write the equation, we equalize the Area that contains a (1st one) and the one from Heron's formula, where we substitute b and c with the values found previously. After simplifying, we should get something like this:

36a=\sqrt{15(15-a)(135-8a)(17a-135)}.

I did't actually bother with trying to solve the equation, but I did graph it using Desmos and found 3 solutions for a
9.071
10.732
20.649

Ignoring the last one (because c would be negative) and substituting both values in the Area formula, after rounding the final answer should be B.
 
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