SOLUTION: Find the area of a regular nonagon of side 6cm

Question 1142081: Find the area of a regular nonagon of side 6cm
Found 4 solutions by josgarithmetic, ikleyn, MathTherapy, Alan3354:
Answer by josgarithmetic(39626)   (Show Source): You can put this solution on YOUR website!
The nonagon has nine of these isosceles triangles:
Peak angle 40 degrees
Each base angle 70 degrees
Let r be distance peak to base angle
Let a be altitude of one isosceles triangle

-

-
Total area of nonagon

----------------------------BELOW STILL WRONG-------------------------------
It has nine of these isosceles triangles:
Peak angle, 40 degrees
Each base angle, 25 degrees--------MISTAKE(Really should be )
Base length, 6 cm
Each congruent side, r, distance from a peak angle to base angle
-

The original figure is made of 18 of these right triangles:
leg r
leg
-
AREA of original figure,
OR

Answer by ikleyn(52858)   (Show Source): You can put this solution on YOUR website!
.

            The "solution" by @josgarithmetic is   W R O N G   from its third line to the end.

            So, for your safety, simply ignore it . . .

            I came to bring the correct solution.

There are 9 congruent isosceles triangles covering the area of the nonagon. The central angle of each triangle is = 40°. Each of the base angle of such a triangle is = 70°. Half of the base length is 3, and the height of each isosceles triangle is h = 3*tan(70°). Thus the area of each isosceles triangle is A = . The area of the nonagon is 9A = = = 222.1 cm^2 (approximately). ANSWER

Completed and solved.

/\/\/\/\/\/\/\/\/

This quasi- and pseudo- tutor @josgarithmetic is a misfortune of this forum.

Having no systematic Math education, he makes errors and provides incorrect solution to each second, third, fourth problem . . .

So, be aware when you get "solutions" from him.

In many (toooooooo many cases) they are wrong.

Do not trust him and always wait for the reaction from other tutors . . .

Answer by MathTherapy(10556)   (Show Source): You can put this solution on YOUR website!
Find the area of a regular nonagon of side 6cm

Correct answer:
One answer is NOT NEARLY CLOSE to being correct - the person is LOST - while the other is close.
Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
Find the area of a regular nonagon of side 6cm
--------
n = 9
s = 6
===========

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You can use that, or you can do the 9 triangles thing.

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