Question

1) Giai 

a) cos²x = 0

b) cos²x = 1

c) cos ( 2x + \(\dfrac{\Pi}{6}\)) = 1

d) cos ( 2x + \(\dfrac{\Pi}{6}\)) = -1

Answer 1

a, \(cos^2x=0\)

\(\Leftrightarrow cosx=0\)

\(\Leftrightarrow x=\dfrac{\pi}{2}+k\pi\)

b, \(cos^2x=1\)

\(\Leftrightarrow2cos^2x-1=1\)

\(\Leftrightarrow cos2x=1\)

\(\Leftrightarrow2x=k2\pi\)

\(\Leftrightarrow x=k\pi\)

Answer 2

c, \(cos\left(2x+\dfrac{\pi}{6}\right)=1\)

\(\Leftrightarrow2x+\dfrac{\pi}{6}=k2\pi\)

\(\Leftrightarrow x=-\dfrac{\pi}{12}+k\pi\)

Answer 3

d, \(cos\left(2x+\dfrac{\pi}{6}\right)=-1\)

\(\Leftrightarrow2x+\dfrac{\pi}{6}=\pi+k2\pi\)

\(\Leftrightarrow x=\dfrac{5\pi}{12}+k\pi\)