Important notes:
3 sides 1 angle - COSINE RULE
2 sides 2 angle - SINE RULE
since, the question wants to find the length of BC. In the end we will have 3 sides and 1 angle and use cosine rule
formula of cosine rule:
a² = b² + c² - 2bc Cos A° (to find the length)
Cos A° = b² + c² - a² / 2bc ( to find the angle, if there is given three sides and have to find the angle)
So just substitute,
a² = 13² + 15² - 2(13)(15) Cos 95°
a = 20.6 or 21
The answer is, (1, -5)...
St meaans s times t
s=-4
t=9
st=-4 times 9
negative times positive=negative
4 times 9=36
-4 time s9=-36
st=-36
answer is -36
