ΔABC is right angled at C with sides AB = 10 cm and AC = 6 cm. Find cosB.
45
In ΔABC, AB = 10 cm and AC=6 cm.
Applying Pythagoras' theorem to ΔABC, we have
AC2+BC2=AB2.
62+BC2=102
⟹BC2=100−36
⟹BC=√64=8 cm
The cosine of an angle is the ratio of the length of the adjacent side to the length of the hypotenuse.
∴cos B=BCAB=810=45