Cosine Law The only way to find the angles in a triangle given the three side lengths is through the Cosine Law The Cosine Law is represented as, {eq}\displaystyle c^2=a^2b^22ab\cos\theta {/eq}Although I asked for the determination of the largest angle of the 3 4 5 triangle (and this visual proof shows the other direction that the hypotenuse is a square on 5), I think the visual intuition is enough to go both directions, that showing a 3 4 rt triangle has hypotenuse 5 is enough (intuitively) to show the 3 4 angle of a 3 4 5 triangleA = α = 368 7 ° = 36°52'12″ = 064 4 rad Angle ∠
Properties Of 3 4 5 Triangles Definition And Uses Video Lesson Transcript Study Com