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# Cosine Rule Help! watch

1. In a triangle ABC, AB=(x-3)cm, BC=(x+3)cm, AC=8cm and angle BAC=60 degrees.Use the cosine rule to find the value of x?

I keep getting an answer of 2 and the answer should be 4.4

Help would be much appreciated..................... ...................
2. You sure the answer is 4.4? I get 4
3. (Original post by vaider)
In a triangle ABC, AB=(x-3)cm, BC=(x+3)cm, AC=8cm and angle BAC=60 degrees.Use the cosine rule to find the value of x?
I keep getting an answer of 2 and the answer should be 4.4
Help would be much appreciated..................... ...................
a²=b²+c²-2bc.cos A
(x+3)²=8²+(x-3)²-(2 x 8(x-3)cos 60)
x²+3x+3x+9=64+x²-3x-3x+9-8x+24
x²+6x+9 - x²-14x+97 = 20x-88
20x=88
x=4.4
4. (Original post by Lil_J)
(x+3)²=8²+(x-3)²-(2 x 8(x+3)cos 60)
Shouldn't that line be:
(x+3)²=8²+(x-3)²-(2 x 8(x-3)cos 60) ?
5. Thanks for your help guys I think I was just getting confused with all the x's and numbers and couldn't manage to tidy them up!

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