# Thread: tan etc

1. ## tan etc

Show that equation 3tanѲ = 2cosѲ

may be written as 2sin²Ѳ + 3sinѲ - 2 = 0

thanks

i think i started it:

3tanѲ = 2cosѲ

3sinѲ/cosѲ = 2(1-sinѲ)

3sinѲ/cosѲ = 2 - 2sinѲ

now i'm stuck

2. Originally Posted by gracey
Show that equation 3tanѲ = 2cosѲ

may be written as 2sin²Ѳ + 3sinѲ - 2 = 0

thanks

i think i started it:

3tanѲ = 2cosѲ

3sinѲ/cosѲ = 2(1-sinѲ)

3sinѲ/cosѲ = 2 - 2sinѲ

now i'm stuck
cos x is NOT equal to 1 - sin x. learn your identities.

when you get to the 3sin(x)/cos(x) = 2cos(x) line, multiply through by cos(x), then replace (cos(x))^2 with 1 - (sin(x))^2 and the rest is routine

3. $\frac{3sin x}{\cos x} = 2 \cos x$

multiply by cosx
$3sin x = 2 \cos^2 x$
$3sin x = 2 (1- \sin^2 x)$
... continue

Bobak

Edit: Jhevon beat me, gosh i wish there was a feature saying who is reply while your typing.

4. Originally Posted by bobak
gosh i wish there was a feature saying who is reply while your typing.
i asked about that once upon a time, it seems everyone has forgotten about it

i'll bring up the issue with the administrators again. *yawn* ...later ...