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  1. Similar Triangles
  2. areas
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Exercise 374
Suppose that $\sin a+\sin b=\sqrt2$ and $\cos a+\cos b=1$. What is $\cos(a-b)$?
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Solution
  1. Squaring and adding: $2+2\cos(a-b)=(\sqrt2)^2+1^2=3$.
  2. $\cos(a-b)=\boxed{\dfrac12}$.
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