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# Can someone help with this maths question please?

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1. http://www.mathsgenie.co.uk/resource...ne-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
2. (Original post by sapphire79)
http://www.mathsgenie.co.uk/resource...ne-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
u can rearrange it to get a^= b^2+c^2-2bcCosA to find the length of a missing side as well
3. (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?
4. (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
5. (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

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