Scalar multiplication
- Scalar multiplication of vector is a process of multiplying a vector by a scalar. A scalar is a number that does not depend on any other quantity in the equation.
- Scalar multiplication does not change the direction, just the length of a vector.
- Lambda of a vector is the scalar value that corresponds to its length. It is represented by the Greek letter “).”
We can also scale vectors. We can stretch them or contract them. If we write something like 2v, it means that the vector has the same direction as v but is 2 times longer. Let’s visualize. [Graph] Suppose that was v. What would 2v look like? It would be in the same direction as v, but twice as long. And that’s 2v. What would be the components of that [v1, v2]? Well, the first component of distance is how far it is. The second component is how high it is. We can determine those ratios by using similar triangles. The small triangle is similar to the big triangle. The hypotenuse of the big triangle is twice as long as the side of the small triangle. 2v is twice as long as v. Therefore, all of the sides should be twice as long. If the corresponding side of the big triangle is 2 times v1, then the side of a small rectangle with the same perimeter is 2 times v1. [Graph] Thus, the components of 2v are 2 times v1 and 2 times v2. 2v->=(2v_1,2v_2) Similarly, a negative vector has a direction opposite to that of vector v and the same length. So negative v looks like that, while positive v is the opposite direction. [Graph] Thus, to sum up, if v is in the same direction as w, this means that v is lambda times w with lambda being a positive number. Any vector that has the same direction as v, say v1 from here to here, is lambda times v. And for the one I’m indicating, lambda would be about 1.5. If v goes in the opposite direction, then v should be lambda times w, where lambda is a negative number. Thus, for example, negative v going in the opposite direction of v, or negative 2v, is going in the opposite direction and twice as long. Now I’ll show you one moment that can be tricky. So is the vector [2, 3] in the same direction as the vector [4, 7]? And how can we determine that? If we see in the same direction, we are likely to think about this. Since the vectors were in the same direction, this meant that v was lambda times w. What we want to know is whether [4, 7] is equal to lambda times [2. 3] for some number of lambda. (4,7)=λ(2,3) If we solve the equation for lambda, then they are in the same direction. And if there is no lambda, if we figure out that no solution exists, it means the two lines are not in the same direction. Now we have lambda times [2,3] is [2 lambda, 3 lambda], exactly like 2v is to [2 v1, 2 v2]. What is the meaning of two vectors being equal to each other? 4=2λ and 7=3λ If we attempt to solve the equation, we will find that the first thing tells us lambda is 2, but the second thing tells us lambda is 7/3. λ=2 but λ=7/3 As a result. all the numbers are different. and there is no constant (lambda) that can be used in the equation to make everything work. And since the vectors for these two functions are not in the same direction, there is no lambda. Here are pictures for us to become even more sure. Their directions do not match. [Graph] In that picture, the black vector is 2 comma 3 and the dotted factor is 4, 7. Although they appear to be moving in the same general direction, the two lines are not exactly parallel. In the diagram on the right, I have added one more red vector, which points in the same direction as 2 and 3. That vector is 4 and 6. So let’s put it down here. Thus, 4 times 6 is 2 times 3. This is in the same direction as 2 times 3. (4,6)=2(2,3) It is the red vector in the picture. The lesson to be learned from this is that whenever we see a question about vectors that involves two things being in the same direction, then algebraically, we can work with that.
