The vertices of a triangle ABC are A(0, 0), B (2, -1) and C (9, 0). Find cos B.

Key points to solve the problem:

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

Given,

Coordinates of 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 =