Question

Select the true statements about half-angle identities.

a)The half-angle identity for cosine is cosA/2 = square root of (1 - cos2A)/2.

b)The half-angle identity for sine is sinA/2 = 2sinAcosA.

c)The half-angle identity for tangent is tanA/2 = 2cos2A - 1.

d)Half-angle identities of cosine, sine, and tangent are in terms of cosine of the whole angle.

Answer 1

b is false since \(\sin(2A)=2\sin(A)\cos(A)\)

Answer 2

okay thank u :)

Answer 3

but do u know which is true?

Answer 4

here is a nice summary of the half angle formulas

Answer 5

http://www.freemathhelp.com/trig-double-angles.html

Answer 6

you can see that the first one is wrong as well

Answer 7

so the answer is d? and are u talking about a being wrong

Answer 8

actually i do not see one what is right hmmm

Answer 9

huh?? lol

Answer 10

the half angle formulas for tangent are in terms of sine and cosine, as you can see

Answer 11

so the last one is wrong

Answer 12

oh no scratch that, the last one is right

Answer 13

ohhh okay soo d :) lol thsnks

Answer 14

you can write
\[\tan(\frac{A}{2})=\pm\sqrt{\frac{1-\cos(A)}{1+\cos(A)}}\]

Answer 15

yes it is d