Question

Explain why cos(-3π/4)=cos(5π/4).

Answer 1

Explanation:

Because the cosine is a positive function from which we can deduce
`\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\la\la\la\la\ddddddddddddddddddddddddddddddddcleverdddddd\ffffffffffffffffffffffffffffffffffffffff\pppppppppppppppppppppppppppppppppppp\dddddd \displaystyle \Large \boldsymbol{Rule : cos(-\alpha)=cos\alpha } \\\\\\ \cos\bigg((-3\pi )/(4) \bigg)=cos135=-sin45=-(√(2) )/(2) \\\\\\cos\bigg((5\pi )/(4) \bigg)=cos225=-sin45=-(√(2) )/(2)` Therefore, they are equal