A problem of vector coordinate operation in senior one Given that the plane vector a = (3,1), the vector b = (x, - 3), and the vector a is perpendicular to the vector B, then what is x? Please give me some advice! The most important thing is the process! The process!

A problem of vector coordinate operation in senior one Given that the plane vector a = (3,1), the vector b = (x, - 3), and the vector a is perpendicular to the vector B, then what is x? Please give me some advice! The most important thing is the process! The process!

Boy, I know you didn't listen to the teacher in class, and you didn't listen to the whole class at all, and you came here after class without asking your classmates
Two vectors
x=(a,b),y=(c,d)
Then the necessary and sufficient conditions for X, y to be perpendicular are as follows:
ac+bd=0
I'll forget it