# triangle trigonometry

• Apr 6th 2008, 08:38 AM
kls7162
triangle trigonometry
http://i111.photobucket.com/albums/n...v_k/img001.jpg

Figure 1 shows the triangle ABC, with AB=6cm, BC=4cm and CA=5cm

a) show that cosA=3/4

b) hence, or otherwise, find the exact value of sinA

thx!
• Apr 6th 2008, 08:45 AM
Mathstud28
here is how I would do this
$c^2=a^2+b^2-2abcos(\theta)$ imput correct values and solve for $\theta$...and for the second one use the law of sines which says that $\frac{a}{sin(A)}=\frac{b}{sin(B)}=\frac{c}{sin(C)}$ where caps are angles and lower case are sides