Question #048a8

1 Answer
Nov 19, 2017

1

Explanation:

sin(a)=-(sqrt(65)/65)

Get the arcsine

A=sin^-1(-sqrt(65)/65)

A=-7.125^o

But angle A is on quadrant III

Get coterminal angle

360-7.125=352.875

Get reference angle

360-352.875=7.125

Get angle on Quadrant III

180+7.125=187.125

Test A if derived angle is correct

sin(-7.125)=-0.124
sin(187.125)=-0.124

Use angle A for half angle identity of cosine

cos(A/2)= sqrt((1+cos(187.125))/2)

Resulting to

=0.998 ~= 1