Prove that the absolute value of a dot product is less than or equal t

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SUMMARY

The discussion centers on proving the inequality |a•c| ≤ |a||c| for any vectors a and c in three-dimensional space. Participants emphasize the importance of understanding the geometric interpretation of the dot product and the magnitudes of the vectors involved. The proof requires manipulating the algebraic expressions for the dot product and the magnitudes of the vectors. Key insights include recognizing that the dot product reflects the cosine of the angle between the vectors, which is crucial for establishing the inequality.

PREREQUISITES
  • Understanding of vector notation and operations, specifically dot products.
  • Familiarity with geometric interpretations of vectors and angles.
  • Knowledge of algebraic manipulation techniques.
  • Basic concepts of vector magnitudes and their properties.
NEXT STEPS
  • Study the geometric interpretation of the dot product in vector analysis.
  • Learn about the Cauchy-Schwarz inequality and its applications in vector mathematics.
  • Explore algebraic proofs involving vector magnitudes and their properties.
  • Practice problems involving the manipulation of vector expressions and inequalities.
USEFUL FOR

Students studying linear algebra, mathematicians interested in vector calculus, and educators teaching vector operations and inequalities.

speny83
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Homework Statement



That is prove that |a•c|≤|a||c| for any vector a=<a1,a2,a3> & c=<c1,c2,c3>


Homework Equations





The Attempt at a Solution



I really don't have much of an attempt at the solution. I am not sure where to start. I can kind of justify it in my mind by saying the sum of two magnitudes will always be a positive number and if 1 of the the a1 c1 etc where negative it could bring the value down but that is no where near a proof.

Where does one even begin to start justifying this?
 
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As always, start out by writing down everything relevant that you know. What is |a•c|? What are |a| and |c|? If you write them out, you will have some algebra to manipulate.
 
lbix asked a perfectly reasonable question. Do you know an expression for the magnitude of the dot product of two vectors? Do you know, for example, what the dot product between two vectors signifies geometrically?
 

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