# Thread: Find the Value of the Number C

1. ## Find the Value of the Number C

Find the value of the number C:

(1/2)[cos^2(x)] + C = (1/4)[cos2(x)]

2. Originally Posted by magentarita
Find the value of the number C:

(1/2)[cos^2(x)] + C = (1/4)[cos2(x)]
Since it's an identity, it's true for all values of x. So substitute a simple value like x = 0. Then solve for C .....

3. Originally Posted by magentarita
Find the value of the number C:

(1/2)[cos^2(x)] + C = (1/4)[cos2(x)]
Cos2x=2(cosx)^2-1 therfor
(cosx)^2=(1+cos2x)/2
as
(1/2)[cos^2(x)] +C=(1/4)[cos2(x)]
1/2((1+cos2x)/2)+C=(1/4)[cos2(x)]
1/4+(cos2x)/4+C=(1/4)[cos2(x)]
1/4+C=0
C=-1/4

4. Originally Posted by nikhil
Cos2x=2(cosx)^2-1 therfor
(cosx)^2=(1+cos2x)/2
as
(1/2)[cos^2(x)] +C=(1/4)[cos2(x)]
1/2((1+cos2x)/2)+C=(1/4)[cos2(x)]
1/2+(cos2x)/4+C=(1/4)[cos2(x)] Mr F says: That red 2 should be a 4.
1/2+C=0
C=-1/2
Actually C = -1/4.

You should have tested it using a simple value of x lol!!

5. ## Ooooopppss

My bad
warning:giving solutions using gprs phone is hazardous to ur(actually mine) calculations.

6. ## Great...

I thank both of you very much.