Answer:
Step-by-step explanation:
2sin²β-7sinβ-4=0
2sin²β-8sin β+1 sin β-4=0
2 sin β(sin β-4)+1(sin β-4)=0
(sin β-4)(2sin β+1)=0
either sin β-4=0
sin β=4 (rejected,as |sin β|≤1)
or
2 sin β+1=0
sin β=-1/2=-sin (π/6)=sin (π+π/6),sin (2π-π/6)
β=7π/6,11π/6
