How to prove that cos(-x) = cos x | How to prove that sin(-x) = - sin x | 𝒆^𝒊𝜽 𝑪𝒐𝒔𝜽 𝒊 𝑺𝒊𝒏𝜽

How to prove that cos(-x) = cos x
How to prove that sin(-x) = - sin x
How to prove tha〖𝒄𝒐𝒔〗^𝟐 𝜽 + 〖𝒔𝒊𝒏〗^𝟐 𝜽 = 𝟏
how to prove that 𝒆^𝒊𝜽 𝑪𝒐𝒔𝜽 𝒊 𝑺𝒊𝒏𝜽
prove,proof of derivative of cos(x),proof of cos x + cos y = 2 cos((x + y)/2) cos((x - y)/2),cos (x + y) = cos x cos y – sin x sin y,proof,proof of cos x + cos y = 2 cos((a + b)/2) cos((a - b)/2),how to find value of x when sin x cos x =1/2?,if sin x cos x = 1/2 then what is the value of x?,cos x + cos y,sin x cos x = ½,(x + xcos x(/(sin x cos x),formula for cos x + cos y,cos(x),cos,cos theta,identity for cos x + cos y,cos(3x) in terms of cos(x)