Question

Given that:

= 2i + 9j ; and ⃗ = -i – 4j . Find . ⃗ ​

Answer 1

A.B = -38

Step-by-step explanation:

A = 2i + 9j and B = -i - 4j.

So, A.B = (2i + 9j).(-i - 4j)

= 2i.(-i) + 2i.(-4j) + 9j.(-i) + 9j.(-4j)

= -2i.i - 8i.j - 9j.i - 36j.j

since i.i = 1, j.j = 1, i.j = 0 and j.i = 0, we have

A.B = -2(1) - 8(0) - 9(0) - 36(1)

A.B = -2 - 0 - 0 - 36

A.B = -38