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

Step-by-step 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

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

Hope this helps you

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step-by-step explanation: