# Math Help - Triangle length question.

1. ## Triangle length question.

Hey, I am stuck on a question and I'd really appreciate an answer with some explaining on how to use it. It would be greatly appreciated. Also, I apologise if there is similar question to this.

"A triangle has two sides of 25cm and 30cm. The angle between the two sides is 30 degrees."
I have found the area, which is: 187.5cm2

I just need to find the other length, which is where I am having difficulty.
Thanks ^____^

2. How did you find the area?

3. In Triangle $\angle ABC$

Area = $\frac{1}{2}\times a\times b\times \sin(C)$

Therefore the poster found the area as follows

Area = $\frac{1}{2}\times 25\times 30 \sin(30 ) \approx 187.4$

To find the other length use the Cosine rule with the values you used to find the area

a = 25
b= 30
C = 30

Cosine rule is

$
c = \sqrt{a^2+b^2-2ab\times \cos(C)}
$

Spoiler:
$c \approx 15$