Question

Thank you！calculate the value of x

Answer 1

x = 3√7 cm.

or 7.94 cm to the nearest hundredth.

Explanation:

We use the Cosine Rule:

21^2 = x^2 + (2x)^2 - 2x.2x cos 120

21^2 = 5x^2 - 4x^2 * -0.5

441 = 5x^2 + 2x^2

7x^2 = 441

x^2 = 63

x = √63

x = 3√7 cm.