In the right angled triangle shown below, if AB=3 cm, BC=4 cm then what is the value of cos A?
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Solution
Since ABC is a right angled triangle, we can apply Pythagoras theorem to get the length of side AC (hypotenuse).
Therefore, AC2=AB2+BC2 ⇒AC2=32+42 ⇒AC2 = 9 + 16 = 25 ⇒ AC = √25 = 5 ⇒ AC = 5
Now, cos A = ABAC = 35.