Question

In triangle ABC measure of angle A equals 45°. The altitude divides the side AB into two parts of 20 and 21 units. Find BC.

Answer 1

In triangle  ABC, BC = 29 units.

Given,

In Δ ABC, ∠A = 45°.

A perpendicular line segment traced from a triangle's vertex to its opposite side is said to be the triangle's altitude.

Let altitude meet AB on D.

So, AD = 20 units and DB = 21 units and ∠ADC = ∠BDC = 90°

In ΔADC,

tan A = DC/AD

tan 45° = DC/20

          1 = DC/20

      DC = 20 units

In ΔBDC,

BC² = BD² + DC²     (Pythagorean Theorem)

      = 21²  + 20²

      = 441 + 400

      = 841

BC  = √841

      = 29  

Hence, BC = 29 units.

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