Question

Find the missing side or angle.
Round to the nearest tenth.

Answer 1

Cosine law
a^2 = b^2 + c^2 - 2(b)(c)cosA
a^2 = 2^2 + 4^2 - 2(2)(4)cos78
a = 4.08
a = 4.1

Answer 2

a = 4.1

Explanation:

To find the missing side in the question, we use the cosine rule

That's

Since we are finding a we use the formula

a² = b² + c² - 2(b)(c) cos A

From the question

b = 2

c = 4

A = 78°

Substitute the values into the above formula

We have

a² = 2² + 4² - 2(2)(4) cos 78

a² = 4 + 16 - 16 cos 78

a² = 20 - 16cos 78

a² = 16.67341

Find the square root of both sides

a = 4.0833

We have the final answer as

a = 4.1 to the nearest tenth

Hope this helps you