2.P(x, y) then vector OP=x vector i+y vector j.

| vector OP|= root sign (x square +y square)

3、P 1(x 1，y 1)P2(x2，y2)

Then the vector p 1p2 = {x2-x 1, y2-y 1}

| vector P 1P2|= radical sign [(x2-x 1) square +(y2-y 1) square]

4. Vector A = {x 1, x2} Vector B = {x2, y2}

Vector a* vector b=| vector a | | vector b | * cos α = x1x2+y1y2.

Cosα= = Vector a* Vector b/| Vector a|*| Vector b|

(x 1x2+y 1y2)

Root number (x 1 square +Y 1 square) * root number (x2 square +Y2 square)

5. Space vector: same as above.

(Hint: Vector A = {x, y, z})