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# Trigonometry- Can Someone Please Explain........ watch

1. Why cos(-B) = cosB but sin(-B) is -sinB..............? thanks!
2. It's because cos is an even function (f(x) = f(-x) - can be seen from the graph)) and sin is an odd function (f(x)=-f(-x)).
3. (Original post by melbourne)
Why cos(-B) = cosB but sin(-B) is -sinB..............? thanks!
for x in [0,2pi]
cos (-x)=cos (2pi-x)=cos(2pi)cos(x)+sin(2pi)sinx=c os x
sin (-x)=sin(2pi-x)=sin(2pi)cosx-cos(2pi)sinx=-sinx
4. (Original post by evariste)
for x in [0,2pi]
cos (-x)=cos (2pi-x)=cos(2pi)cos(x)+sin(2pi)sinx=c os x
sin (-x)=sin(2pi-x)=sin(2pi)cosx-cos(2pi)sinx=-sinx
cheers guys!

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