In a triangle ABC, ∠A = 60°, AB = 6 cm, and AC = 4 cm. Find BC.

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  1. \(\frac{2}{\sqrt{7}}\) cm
  2. \(\frac{3}{\sqrt{5}}\) cm
  3. \(\frac{7}{\sqrt{7}}\) cm
  4. \(\frac{5}{\sqrt{5}}\) cm

Answer (Detailed Solution Below)

Option 1 : \(\frac{2}{\sqrt{7}}\) cm
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Detailed Solution

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Given:

In triangle ABC,

∠A = 60º

AB = 6 cm

AC = 4 cm

Formula Used:

Using the Cosine Rule:

BC2 = AB2 + AC2 - 2 × AB × AC × cos(∠A)

Calculation:

Substitute the values:

AB = 6, AC = 4, cos(60º) = 1/2

⇒ BC2 = 62 + 42 - 2 × 6 × 4 × (1/2)

⇒ BC2 = 36 + 16 - 24

⇒ BC2 = 28

⇒ BC = √28

⇒ BC = √(4 × 7)

⇒ BC = 2√7

⇒ BC = (2/√7) cm

The correct length of BC is (2/√7) cm.

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