I have to prove the following statement.
1+cos2π5+cos4π5+cos6π5+cos8π5=0
I have tried to use the sum of angles formula for cosine, but didn't get to a point where I'd be able to show that it is equal to 0.
How to find limh→0sin(ha)h without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...
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