# Thread: Proof in a triangle.

1. ## Proof in a triangle.

Proof AB=3.6sin0.2

i've done.

$\frac{a}{sin0.4} = \frac{1.8}{sin1.37}$

$\rightarrow a=\frac{1.8sin0.4}{sin1.37}$

but duno how to derive the answer.

thanks!

2. Originally Posted by BabyMilo
Proof AB=3.6sin0.2

i've done.

$\frac{a}{sin0.4} = \frac{1.8}{sin1.37}$

$\rightarrow a=\frac{1.8sin0.4}{sin1.37}$

but duno how to derive the answer.

thanks!
Use the cosine rule instead.

3. Originally Posted by Prove It
Use the cosine rule instead.
Still I dont understand how i would dervie the required.

$a=\sqrt{2*1.8^2-2*1.8*1.8cos0.4}$

They are not whole numbers so how would i find the required. and since this is in cos.

thanks!

4. Is it just,

$a=\sqrt{2*1.8^2-2*1.8*1.8cos0.4}$
$a=\sqrt{2*3.24-3.6*1.8(0.921)}$
$a=\sqrt{2*3.24-3.6*1.65}$

Or is there something I'm not getting D:

5. Originally Posted by BabyMilo
Proof AB=3.6sin0.2

i've done.

$\frac{a}{sin0.4} = \frac{1.8}{sin1.37}$

$\rightarrow a=\frac{1.8sin0.4}{sin1.37}$

but duno how to derive the answer.

thanks!
Solve it nevermind.

cut the triangle into half.

so it's 1.8sin0.2 x 2
=3.6sin0.2 as required.

haha.