# Math Help - Sine and Cosine rules

1. ## Sine and Cosine rules

Hello Everyone,
I would really appreciate if someone could help me with this question.

In a triangle ABC, c=7, b=8 and C=60degrees
(a) Use Cosine rule to write down a quadtratic equation involving a
(b) Hence solve it
(c) Use Sine rule to find two values of a(first find B and so A) and compare these with your answers in part(b)

I have no idea what the question really means. Any sort of help would be really appreciated

2. Just to help you along a bit, here is the Sine rule for triangle abc with angles A, B, C:

$\frac{a}{\sin{A}} = \frac{b}{\sin{B}} = \frac{c}{\sin{C}}$

3. Angle C = 60 degrees.

Use:

$c^2=a^2+b^2-2ab\cos C$

$7^2=a^2+8^2-2a(8)\cos 60$

$49=a^2+64-8a$

$a^2-8a+15=0$