Question

If the sin(50) = 10/15 what is cosine(40)?
Can someone explain this to me ...

Answer 1

Recall that


`\cos(90-x)^\circ=\sin x^\circ`

which tells you that
`\cos40^\circ=\cos(90-50)^\circ=\sin50^\circ`, so in fact


`\cos40^\circ=\sin50^\circ=(10)/(15)`

Attached is an image demonstrating why the identity is true.