Modulus stands for length!

If the vector is on the X, Y axis, the modulus of oa (0 0,3) is 3!

AB 2 becomes an ordinary point!

A(x，y)B(x 1，y 1)

AB vector (x 1-x, y 1-y)

The module draws a right triangle, with the distance between two points in the horizontal position AB |x 1-x|=a and the vertical distance span | y1-y | = b.

Right triangle is established!

Pythagorean theorem gives |AB|, that is, the modulus of AB =V (a? +b？ )

(-a)？ =a？ ! ! !

So you can take the absolute value away!