How to judge the shape of triangle by vector method We should be scientific and advanced

An obtuse triangle is a product of three vectors less than zero
Greater than zero is an acute triangle
Equal to zero is a right triangle

RELATED INFORMATIONS

1. What does the normal vector of a plane mean?
2. How to find normal vector and direction vector? For example, 5x + 6y-1 = 0, how can we easily see the normal vector and direction vector of this equation?
3. Normal vector direction of space surface Space surface f (x, y, z) = 0. Its normal vector is (FX ', FY', FZ '). What is its direction? How to determine the direction of the normal vector? For example, the space curve X = x (T), y = y (T), z = Z (T), its tangent X '(T), y' (T), Z '(T) direction is consistent with the point's moving direction when t increases. Similarly, I think there should be a conclusion for the space surface! What is that?
4. Is the concept of the same direction in vector different from that in plane geometry?
5. Space geometric vector It is known that the radius of the circumscribed sphere o of the triangular pyramid P-A B C is 1 and satisfies the vector OA + ob + OC = 0 Then the volume of the regular triangular pyramid P-A B C?
6. Find the normal vector (urgent)! Known surface equation is x ^ 2 + 2Y ^ 2 + 3Z ^ 2 = 15, find the normal vector
7. Application of vector method How to use vector to show plane parallel
8. On vector operation There are dot multiplication and cross multiplication in vector operation. What's the difference and connection between them? For example, in the moment M = f * l, why can't dot multiplication be used instead of cross multiplication? I know that the direction is determined by the right-hand screw rule. Is the size a simple multiplication?
9. Vector computing Vector contains direction and size, but with direction operation does not change the size of it?
10. How to calculate the vector product vector a * vector b (how to determine the size and direction) Note that * is not a dot product, and the result is not a number, but a vector Take the operational expression of physical quantities such as moment and angular momentum as an example
11. How to calculate the triangle rule of physics?
12. How to use trigonometric parallax method to calculate planetary distance? Where does this distance go from?
13. Triangle rule of vector addition How to derive the triangle rule of vector addition? Isn't the sum of two sides of a triangle greater than the third side? Why is vector addition OK? Even if vector addition is pseudo mechanics, isn't that a bit misleading
14. If 3x = 2Y, then 6-3x + 2Y=
15. Is voltage scalar or vector?
16. Is work scalar or vector?
17. Why is magnetic flux scalar
18. Is power p a scalar or a vector? Why is there no direction? P = f / T, isn't f a vector? Is the dot product of two vectors scalar? Why?
19. Are magnetic flux and magnetic field intensity vector or scalar respectively? Why?
20. Is work a vector or a scalar? Why According to w = flcosa Where f and L are all vectors, is the resulting w also a vector? Excuse me, if the right direction is defined as the positive direction, the object is still on the horizontal table, it is pulled 5 N horizontally to the left, and the object moves 5 m to the left, then the work done by the pulling force on the object is w = FS = 5 * - 5 = - 25J So, what force does is not negative work? And the pulling force is the motive force. According to the principle, we should do positive work. How to explain? Good answer, increase the reward