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Suppose that vand ware unit vectors. If the angle between vand iis α and that between wand iis β, use the idea of the dot product v·wto prove that

cosα-β=cosαcosβ+sinαsinβ

Short Answer

Expert verified

It is proved thatcosα-β=cosαcosβ+sinαsinβ.

Step by step solution

01

Step 1. Given Information

there are two unit vectors vand w.The angle between vand iis α and that between wand iis β. We have to use the idea of dot product and prove that
cosα-β=cosαcosβ+sinαsinβ.

02

Step 2. Proving

If vand ware unit vectors.

So, v=1,w=1.

Now, the dot product of

v·w=vw³¦´Ç²õθv·w=³¦´Ç²õθv=1,w=1

When θ=α-βorβ-αwe get,

v·w=³¦´Ç²õθv·w=cosα-β........(a)

Now,

v=v³¦´Ç²õαi+²õ¾±²Ôαjv=³¦´Ç²õαi+²õ¾±²Ôαjv=1

And

w=wcosβi+sinβjw=cosβi+sinβjw=1

So, cosα-β=v·wcosα-β=³¦´Ç²õαi+²õ¾±²Ôαj·³¦´Ç²õβi+²õ¾±²Ôβjcosα-β=³¦´Ç²õ᳦´Ç²õβ+²õ¾±²Ôα²õ¾±²Ôβ

Hence proved.

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