Sentence:  The right-hand side of the <WSD>quaternion</WSD> equation requires scalar multiplication and <WSD>quaternion</WSD> addition. 
Meaning of the word marked with <WSD> tags:  A four-dimensional hypercomplex number that consists of a real dimension and 3 imaginary ones ("i", "j", "k") that are each an independent square root of -1. They are commonly used in vector mathematics and in calculating the rotation of three-dimensional objects.