Question

Evaluate the dot product of (5,7) and (-8,2)

Answer 1

You have to multiple and then add to get
(5)(-8)+(7)(2)=-26

Answer 2

A=Point (5,7) when represented in terms of vector = 5 i + 7 j

B=Point (-8,2) ,when represented in terms of vector = -8 i + 2 j

Dot Product of two vectors = A.B

Keep in mind

1.⇒i.i=1, j.j=1,i.j=j.i=0

2.Dot product of two vectors is Scalar Quantity.

So,→ A. B= (5 i + 7 j) . (-8 i +2 j)

= 5 × -8 +7 × 2

= -40 +14

= -26