Question

c) Without using calculator find the v alue of sin ( -765°)

Answer 1

since sin(-0)=-sino
sin(-765°)=sin(765)
=-sin[(9×90°)-45°]
=-cos(45°)
=
$\frac{1}{ \sqrt{2} }$
because of [9×90°;;;; odd×90°,sin changes to -cos and(9×90°)-45°, it is in 1st quadrant::: it is positive