Question

Solve for sin a/2 when cos a=4/5 , o 11 years ago

Answer 1

just to check i got

\[\frac{ 3\sqrt{10} }{ 10 }\]

Answer 2

correct?

Answer 3

and wouldn't cos/2 be the same thing?

Answer 4

I guess you would use the identity cos a = 1 - 2 sin^2 (a/2) ?

Answer 5

how did you get the 3?

Answer 6

I just used the half angle formula

Answer 7

oh - i cant remember that one lol

Answer 8

I got sqrt10/10 using my formula. Again its a while since I did trig....

Answer 9

@Nnesha

Answer 10

cosa = 1 - 2 sin^2 (a/2)
4/5 = 1 - 2 * 10/100
4/5 = 1 - 1/5

Answer 11

so it does fit

Answer 12

ohhh, your saying that the answer is sqrt of 1/10?

Answer 13

if so , I see what i did wrong, i'm suppose to subtract not add 5+4

Answer 14

so cos/2 would be \[\frac{ 3\sqrt{10} }{ 10 }\]

sin/2=\[\sqrt{\frac{ 1 }{ 10 }}\]

Answer 15

@welshfella

Answer 16

yes

Answer 17

so both those are correct?

Answer 18

yes

Answer 19

now i need to solve for tan /2

Answer 20

im actually getting just 1/3

Answer 21

oh - now i definitely cant remember the tan/2 formula , i'm afraid

Answer 22

looks a lot easier actually

Answer 23

im just getting

(3/5)/1+4/5=1/3

Answer 24

yea - they are vaguely familiar lol

Answer 25

are you able to do it?

Answer 26

@TheSmartOne

Answer 27

yes 1/3 is correct

Answer 28

ok ty