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Is it a necessary and sufficient condition or a necessary and insufficient condition that the direction vectors of two parallel lines are parallel? Are the normal vectors of two parallel lines equal rt
If the direction vectors of two lines are parallel, it is necessary and sufficient that the two lines are parallel
The normal vectors of two parallel lines are equal. This sentence is wrong. There are innumerable normal vectors of a line on the plane perpendicular to the line (the line drawn from a point on the plane is the intersection of the line and the plane), so they are not equal
If you know the coordinates of two vectors, how to find their point multiplication
Or modular multiplication
Is modular multiplication the same
A (a, b) dot times b (C, d) = AC + BD
|A | * | B | = each module is calculated first and then multiplied, so it's different
If the vector a = (1, - 2), | B | = 4 | a |, and a and B are collinear, then B may get the coordinates (- 4,8)
If the vector a = (1, - 2), | B | = 4 | a |, and a and B are collinear, then the coordinates of B may be (- 4,8)
b=±4a=±(4,-8)
How to judge the direction of two vectors represented by coordinates?
For example, a vector = (- 2, - 1)
B vector = (2,1)
Is it to draw a picture directly?
Thank you for your reply
So what if a = (- 1,2) B = (1,6)?
The direction indicated by coordinates starts from a dot (0,0). We can see it clearly by sketching
If you don't draw a picture, it's OK. The angle formed by the vector in the positive direction of the lower axis, such as a, is related to the coordinates
When x > = 0, a = arctan (Y / x)
In X
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