The value of vector |q-r| = 18
The Cosine Rule can be used in any triangle relate all three sides to one angle.
Let OA =|q|
OB = |r|
BA = |q|-|r|
Hence ∠AOB = 45°+(360°-300)
∠AOB = 45°+60°
∠AOB = 105°
Given |q| = 5, |r| = 16
Now using cosine rule
|q-r| = √(16)²+(5)²-2×16×5×cos105°
|q-r| = 18
Learn more about Cosine Rule
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