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Can someone help with this maths question please?

http://www.mathsgenie.co.uk/resources/104_sine-cosine-areaans.pdf
It's the last question
Okay so I understood how they found the angle C, but then how did they use the cosine rule to find the missing side? I thought you could only use the cosine rule when you had an angle enclosed by 2 sides :confused:

Thanks in advance :smile:

Reply 1

qwerty0301

Original post by sapphire79

Thanks in advance :smile:

u can rearrange it to get a^= b^2+c^2-2bcCosA to find the length of a missing side as well

Reply 2

sapphire79

Original post by qwerty0301

u can rearrange it to get a^= b^2+c^2-2bcCosA to find the length of a missing side as well

How is the missing side a when the side opposite the angle A is a?

Reply 3

qwerty0301

Original post by sapphire79

How is the missing side a when the side opposite the angle A is a?

U can call any sides A,B or C but if u want u can also rearrange the equation to get:
c^2= a^2+b^2-2abCosC or b^2= a^2+c^2-2acCosB

I prefer doing that myself tbh

Reply 4

sapphire79

Original post by qwerty0301

U can call any sides A,B or C but if u want u can also rearrange the equation to get:
c^2= a^2+b^2-2abCosC or b^2= a^2+c^2-2acCosB

I prefer doing that myself tbh

Thanks