Question

Cos² y– sin²y=1–2sin² y

simplify pls, urgent​

Answer 1

cos²y - sin²y = 1 - 2sin²y

or, cos²y - sin²y + 2sin²y = 1

or, cos²y + sin²y = 1 [It's a formula]

(Is that what you mean by simplify?)

Answer 2

Explanation:

Cos²y + Sin² y = 1

Therefore, Cos² y = 1 - Sin² y

LHS = Cos² y - Sin² y

= 1 - Sin² y - Sin² y {Combine like terms}

= 1 - 2sin² y = RHS