Question

prove that sin (270° + A) = -cosA​

Answer 1

Answer:

$sin (270° - θ) = - cos θ, [since sin (90° - θ) = cos θ]$

$cos (270° - θ) = cos [180° + 90° - θ]$

$= cos [180° + (90° - θ)]$

$= - cos (90° - θ), [since cos (180° + θ) = - cos θ$

Therefore, $cos (270° - θ) = - sin θ, [since cos (90° - θ) = sin θ]$

hope it helps you...

mark it as brainliest...

Answer 2

sin(270+A) = sin(360-(90-A))

360-(90-A) will be in 4th Quadrant

sin(360-(90-A)) = -sin(90-A)

90-A will be in 1st Quadrant

-sin(90-A) = -cosA