Let magnitude of vector r is equal to 17 at an angle of 40 degrees and magnitude of vector s is equal to 14 at an angle of 160 degrees Which expression represents magnitude of vector r plus vector s ?

The angle between the vectors is 160° − 40° = 120°. The magnitude of their sum is √(17² + 14² + 2·17·14 cos 120°). Since cos 120° = −cos 60°, this is the same as √(17² + 14² − 2·17·14 cos 60°), which is choice D.

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