- #1

SeReNiTy

- 170

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-1 < [tex] \frac{a.b}{\|{a}\|\|{b}\|}} [/tex] > -1

I did this by using the cosine rule which is [tex] c^2 = a^2 + b^2 - 2a.b\cos{\vartheta} [/tex]

How ever our teacher did it by a scharts proof which i don't quite understand, , Now my question is why can't i prove it using the cosine rule and could somebody explain the schwartz proof a bit better?