? Range in Double-Angle Identity

ukumure

New member
Joined
Jan 11, 2021
Messages
15
Hi! I'm trying to help my friend but we're both stuck in the middle of the process! We tried using Double-Angle Identities and got different answers from the given answer (photo attached below). Anyone can help us solve this problem? It would be a big help for her today. Thank you so much!

1.png
 
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