Multiplication (or product) of two vectors is defined in two ways, namely, dot (or scalar) product where the result is a scalar, and vector (or cross) product where the result is a vector. Based on these two types of products for vectors, we have various applications in geometry, mechanics, and engineering. In real life, we use dot product when installing a solar panel on a roof.
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In this article, we will cover the concept of Dot Product Of Two Vectors. This topic falls under the broader category of Vector Algebra, which is a crucial chapter in Class 11 Mathematics. This is very important not only for board exams but also for competitive exams, which even include the Joint Entrance Examination Main and other entrance exams: SRM Joint Engineering Entrance, BITSAT, WBJEE, and BCECE. A total of fourty five questions have been asked on this topic in JEE Main from 2013 to 2023 including two in 2021.
The dot product of two vectors is the product of the magnitude of the two vectors and the cos of the angle between them.
If
Dot Product: Formula
If
1.
2.
3.
4.
5.
If
1.
2.
(distributive )
3.
4.
For any two vectors
(I)
(ii)
(iii)
(iv)
The angle between two vectors is calculated as the cosine of the angle between the two vectors. The cosine of the angle between two vectors is equal to the sum of the products of the individual constituents of the two vectors, divided by the product of the magnitude of the two vectors. The formula for the angle between the two vectors is given by
The dot product of two vectors is constructed by taking the component of one vector in the direction of the other and multiplying it with the magnitude of the other vector. To understand the vector dot product, we first need to know how to find the magnitude of two vectors, and the angle between two vectors to find the projection of one vector over another vector.
A vector represents a direction and a magnitude. The magnitude of a vector is the square root of the sum of the squares of the individual constituents of the vector. The magnitude of a vector is a positive quantity.
For a vector,
The dot product is useful for finding the component of one vector in the direction of the other. The resultant of a vector projection formula is a scalar value.
Let
Draw
From triangles
Here OL and OM are known as projections of
Now,
Thus. geometrically interpreted, the scalar product of two vectors is the product of the modulus of either vector and the projection of the other in its direction.
Thus,
Projection of
If the two vectors are expressed in terms of unit vectors, i, j, k, along the x, y, and z axes, then the scalar product is obtained as follows:
For any two non-zero vectors
As
Example 1: Let S be the set of all
Solution
For
Let
For
Hence, the answer is
Example 2: Let a vector
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Solution
This should hold
Hence, the answer is
3
Example 3: In a triangle ABC , if
Solution
Clearly projection of AB on BC is
To get
Hence, the correct option is
The scalar product, or dot product quantifies the relationship between vectors through both geometric insight and numerical calculation. Its properties of commutativity, distributivity, and facilitation of projection make it indispensable in fields ranging from physics and engineering to computer graphics. Knowledge of the scalar product helps in solving problems and advancing knowledge.
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