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# C2 help! watch

1. 6) In triangle ABC, AB=x cm, BC=5cm and AC=(10-x)cm:

Show that cos angle ABC=4x-15/2x

Where I have written cos angle it is shown in the book by a little triangle symbol with the right side missing, hope it actually means angle haha.

thanks
2. you use a re-arrangement of the cosine rule.. so cos ABC = (AB)^2 + (BC)^2 - (AC)^2 all devided by 2*AB*BC .... and just sub in the number and you should get the answer (Btw ^2 means sqaured :P )

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Updated: February 1, 2010
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