# Question #85311

##### 1 Answer

Resultant

#### Explanation:

We use the technique called the **cosine rule**(or the rule of cosines)

Imagine, that the parrallelogram on the far right of the picture were divided into 2 equal triangles.

Now say, the sides were labelled

Then the cosine rule could be stated as:

In our case, we can apply the rule thus:

Applying the rule: