In a ` Delta A B C ,` prove the following :If `a=18 ,\ b=24 ,\ c=30` , find `cos A ,\ cos B\ a n d\ cos Cdot`

Explanation

In a `triangle {ABC}`, we have

`cos A=frac{b^{2}+c^{2}-a^{2}}{2 b c}`

`cos B=frac{a^{2}+c^{2}-b^{2}}{2 a c}`

`cos C=frac{a^{2}+b^{2}-c^{2}}{2 a b}`

we have,

`a=18, b=24, c=30`

Therefore,

`cos A=frac{b^{2}+c^{2}-a^{2}}{2 b c}=frac{1152}{1440}=frac{4}{5}`

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