Prove x=(2nπ+π2) or x=2nπ, where n∈I.
cos x+sin x=1⇒1√2cos x+1√2sin x=1√2
⇒cosxcosπ4+sinxsinπ4=1√2
⇒cos(x−π4)=cosπ4
⇒x−π4=2nπ±π4
⇒x−π4=2nπ+π4 or x−π4=2nπ−π4
⇒x=2nπ+π2 or x=2nπ, where n∈I.
solve the inequality cos x ≤ −12
The general solution to sin10x+cos10x=2916cos42x is