Question

Prove that this relationship is true (Image Attached)

Answer 1

From the picture, we can see that

$\sin\theta=\dfrac HB\implies\dfrac{\sin\theta}C=\dfrac H{BC}$

$\sin\beta=\dfrac HC\implies\dfrac{\sin\beta}B=\dfrac H{BC}$

which means

$\dfrac{\sin\theta}C=\dfrac{\sin\beta}B$