In △ABC,a=13, b=14, and c=18. Then angle, m∠A is is 46.654°
<h2>Further Explanation;</h2>
- In a triangle ΔABC, with sides a, b, and c, and angles ∠A, ∠B, and ∠C can be solved using sine rule or cosine rule.
<h3>Sine rule </h3>
- This rule is used when one is given two sides of the triangle and an angle, or one side and two angles are known.
- According top sine rule;

<h3>Cosine rule </h3>
- Cosine rule is used when all the sides of the triangle are known or when two sides of a traingle and an angle are known.
- According to cosine rule;
or
or

In our case;
we are going to use Cosine rule to find m∠A
We are given;
a=13, b=14, and c=18
Therefore;

Replacing the variables;

Making CosA the subject;





Therefore; In △ABC,a=13, b=14, and c=18, m∠A is 46.654°
Keywords: Sine rule, Cosine rule
<h3>Learn more about: </h3>
Level; High school
Subject: Mathematics
Topic: Triangles
Sub-topic: Cosine and sine rule