a) `(2sinx-1)(cosx+2) =0`
`<=>` \(\left[ \begin{array}{l}2sinx-1=0\\cosx=-2(VN) \end{array} \right.\)
`<=> sinx = 1/2`
`<=> sinx = sin π/6`
`<=>` \(\left[ \begin{array}{l}x=\dfrac{π}{6}+k2π\\x=\dfrac{5π}{6}+k2π\end{array} \right.\)
b) `2cos2x = \sqrt3`
`<=> cos2x = cos π/6`
`<=> 2x = \pm π/6 + k2π`
`<=> x= \pm π/12 + kπ`
c) `cosx=sinx`
`<=> cosx/sinx = 1`
`<=> cotx=1`
`<=> x = π/4 + kπ`