Question

Solve cos 2 θ = cos θ + 2 for 0 < θ < 2p

Answer 1

@ikram002p what would we do in this situation

Answer 2

is it
\(\Huge \cos^2 \theta \)
or
\(\Huge \cos 2 \theta \)

Answer 3

it is cos 2θ

Answer 4

so could we divide cos θ on each side and it would be θ=2

Answer 5

@ikram002p what happens

Answer 6

sry my account acting weird :-|

Answer 7

so lets do it
cos 2θ = 2 cos^2 θ -1
right ?

Answer 8

cos 2 θ = cos θ + 2
2 cos^2 θ -1 = cos θ + 2

Answer 9

no Solve cos 2 θ = cos θ + 2 for 0 < θ < 2p

Answer 10

ya

Answer 11

i know i know
but
cos 2 θ = 2 cos^2 θ -1

Answer 12

did u got this one ?

Answer 13

no i don't

Answer 14

shall i keep going ?

Answer 15

ok ill tell you what it is

Answer 16

why does it become from cos 2 θ = cos θ + 2 to
cos 2 θ = 2 cos^2 θ -1

Answer 17

do u know this rol
cos^2 + sin^2=1 ??

Answer 18

no

Answer 19

ohh u dnt know it :-\

Answer 20

ok u know
how to solve
cos (A+B ) ??

Answer 21

ya

Answer 22

so from cos 2 θ = cos θ+2 what will we do next

Answer 23

ughh no !

Answer 24

cos 2 θ = cos ( θ+θ) right ??

Answer 25

ya

Answer 26

cos ( θ+θ) = cos θ cos θ - sin θ sin θ
right ?

Answer 27

yup

Answer 28

cos 2 θ = cos ( θ+θ)=cos^2 θ - sin^2 θ
u agree with this untill nw ?

Answer 29

ya

Answer 30

ok now
use this law ( u have to memorise it )
cos^2 θ + sin^2 θ=1
ok ?

Answer 31

can we subtract cos θ from one side to the other so the equation can be become cos θ=2

Answer 32

then θ=cos^-1(2)

Answer 33

no u cant coz u have 2thata in one side and theta in the sec side

Answer 34

u agree to that ?

Answer 35

ya

Answer 36

u only can remove it when both angels are the same ok ?