54 I was wong on A and C Not sure what I did wrong A For the

5.4 I was wong on A and C... Not sure what I did wrong.

For the following, assume that all the given angles are in simplest form, so that if A is in QIV you may assume that 270°

cos A=1/2

sin(A/2)=+-sqrt(1-cosa)/2

=+- sqrt(1-1/2)/2=+-sqrt 1/4=+- 1/2

and since the quadrant is fourth

therefore sin(A/2) is positive

hence sin(A/2)=1/2

c. sin A=3/5 A is in second quadrant and in second quadrant cos is negative

Therefore cos A= -4/5

cos(A/2)=+-sqrt(1+cosA)/2= +-sqrt(1-4/5)/2= +- sqrt 1/10

cos(A/2)=-1/sqrt10 or -sqrt10/10