Key points to solve the problem:

• The idea of distance formula- Distance between two points P(x₁,y₁) and Q(x₂,y₂) is given by- PQ =

Given,

Coordinates of the triangle and we need to find cos B which can be easily found using cosine formula.

See the figure:

From cosine formula in ΔABC , We have:

cos B =

using distance formula we have:

AB =

BC =

And, AC =

∴ cos B = …ans