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!

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- Apr 6th 2008, 07:38 AMkls7162triangle 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, 07:45 AMMathstud28here is how I would do this
$\displaystyle c^2=a^2+b^2-2abcos(\theta)$ imput correct values and solve for $\displaystyle \theta$...and for the second one use the law of sines which says that $\displaystyle \frac{a}{sin(A)}=\frac{b}{sin(B)}=\frac{c}{sin(C)}$ where caps are angles and lower case are sides