You are watching: Cos(2θ) = cos θ

No, they room not the same.

When you kind $cos^2 heta$ girlfriend actually median $(cos heta)^2$.

When you type $cos heta^2$ you typical $cos( heta ^2)$.

The very first notation is provided to mean$$cos^2 heta = left( cos heta ight)^2$$Your second notation will usually be review as$$cos heta^2 = cos left( heta^2 ight)$$although it is sometimes desired to usage the notation in the right-hand next to be clear.

They space not the very same since$$left( cos heta ight)^2 = cos hetacos heta e cos( heta heta) = cos( heta^2)$$

It"s a matter of syntax.

In handwriting or literature: $sin^2 x equiv (sin x)^2$ and also $cos x^2 equiv cos (x^2)$;

however for computer software, say ** rwandachamber.orgematica**:

**Cos $^2$** refers to $(cos x)^2$ while

**Cos**describes $cos (x^2)$.

Should be very careful.

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Trigonometric identity: $frac an heta1-cot heta+frac cot heta1- an heta =1+sec hetacdotcsc heta$