1. ## Triangle height?!

i need urgent help!!!

i need a formula for this question...

In this diagram, the area of a pentagon is 800 square centimeters.

What is the area of the green part, in square centimeters? Please round up to the nearest whole number, and submit only the answer.

i found the side length of the pentagon to be
21.56cm

2. ## hmmm

i understand that the formula for the area of a triangle is (b*h)/2

if got the base, i just dont know how to find the height... can anyone help?

3. Hello, himachuu!

In this diagram, the area of a pentagon is 800 square centimeters.

What is the area of the green triangle in cm² ?
Round up to the nearest whole number.

i found the side length of the pentagon to be 21.56cm. . . . . Good!

An interior angle of a regular pentagon is 108°.
Hence, a base angle of the green isosceles triangle is 72°.

The height of the triangle is: .$\displaystyle h \:=\:\frac{21.56}{2}\tan72^o \:\approx\:66.35$ cm.

4. Hopefully it will help if I remind you that each interior angle in a pentagon is 108 degrees, so each exterior angle is 72...

See if you can find your height using $\displaystyle \tan(72)$.

5. Originally Posted by Soroban
Hello, himachuu!

An interior angle of a regular pentagon is 108°.
Hence, a base angle of the green isosceles triangle is 72°.

The height of the triangle is: .$\displaystyle h \:=\:\frac{21.56}{2}\tan72^o \:\approx\:66.35$ cm.

so basically all i need to do is go...

(66.35 * b)/2?

thank you sooo much ^^

6. Soroban!!! That's twice tonight!!!