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The second question:

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The third question:

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This part of the extended materials mainly examines the knowledge points of vectors:

It can be imagined as a line segment with an arrow. The arrow indicates the direction of the vector; Line segment length: indicates the size of the vector. The quantity corresponding to a vector is called a quantity (called a scalar in physics), and a quantity (or scalar) has only a size and no direction.

Vector notation: print letters (such as A, B, U, V) in bold, and add a small arrow "→" at the top of the letter when writing. If the starting point (a) and the ending point (b) of the vector are given, the vector can be recorded as AB (and added to the top →). In the space Cartesian coordinate system, vectors can also be expressed in pairs. For example, (2,3) in the xOy plane is a vector.

In the plane rectangular coordinate system, two unit vectors I and J with the same direction of X axis and Y axis are taken as a set of bases. A is an arbitrary vector in a plane rectangular coordinate system, with the coordinate origin O as the starting point and P as the end point. According to the basic theorem of plane vector, there is only one pair of real numbers (x, y), which makes a=xi+yj. Therefore, the pair of real numbers (x, y) is called the coordinate of vector A, and is denoted as a=(x, y). This is the coordinate representation of vector A, where (x, y) is the coordinate of the point. Vector a is called the position vector of point p.