Which of the following can not be evaluated using the double angle formulas and explain why.

a. 2 sin75 cos75
b. 1 - 2 sin^2 3pi/8
c. (2 tan 15)/(1 - tan^2 15)
d. 2 cos^2 12 -1

Question

Which of the following can not be evaluated using the double angle formulas and explain why.

a. 2 sin75 cos75
b. 1 - 2 sin^2 3pi/8
c. (2 tan 15)/(1 - tan^2 15)
d. 2 cos^2 12 -1

xapproachesinfinity · Answer

2cos75sin75=sin(2*75)=sin(150) can be evaluated
1-2sin^2(3pi/8)=cos(2*3pi8)=cos (3pi/4) also can be evaluated
follow the same reasoning tell you find the needed one

anonymous · Answer

Oh snap I didn't notice the 2 in the numerator for the last one, therefore it can't be evaluated. Thanks for that!

xapproachesinfinity · Answer

last one didn;t have any denominator so i don;t get why you mentioned numerator

anonymous · Answer

second last one*

anonymous · Answer

no wait hold up

anonymous · Answer

i was looking at the wrong formula, c can be tan30x and d can be cos 24x so im assuming the last one because we don't know any special triangles that have 24 of 12 in their angles?