Question

cos(2theta-pi/2=-1

Answer 1

remember that cosine is -1 in the negative x-axis

Answer 2

is it this ?


\(\large\tt \begin{align} \color{black}{cos(2\theta-\dfrac{\pi}{2})=-1}\end{align}\)

Answer 3

@mathmath333 try to check the answer you'll end up with cosine zero which is '1'

Answer 4

i dont know

u can show ur work and correct my answer

Answer 5

\[\cos (2\theta - \frac{ \pi }{ 2 }) = -1\]
using the difference of the cosine of two angles cos(A-B)=cosAcosB+sinAsinB
you'll have:
\[\cos2 \theta \cos \frac{ \pi }{ 2 } + \sin2 \theta \sin \frac{ \pi }{ 2 } = -1\]
cosine pi/2 or 90degrees is zero. it will be cancelled out
sin pi/2 = 1
\[\sin 2 \theta = -1\]
\[2 \theta = \sin^{-1} (-1)\]
remember that when sine is -1, it lies in 270degrees or 3pi/2
\[2 \theta = \frac{ 3 \pi }{ 2 }\]
\[\theta = \frac{ 3 \pi }{ 2(2) }\]
\[\theta = \frac{ 3 }{ 4 } \pi\]

Answer 6

@cc1125 please refer to the unit circle i attached above

Answer 7

oh i think ur method is optimum and correct here