Question

If O be the origin and if P₁ (x₁, y₁) and P₂(x₂,y₂) be two points, then (OP₁. OP₂) cos (ŠP₁OP₂) is equal to-

• A. x₁y₂ + x₂y₁
• B. (x₁² + y₁²) (x₂² + y₂²)
• C. (x₁ – x₂)² + (y₁ – y₂)²
• D. x₁x₂ + y₁y₂

Answer 1

Answer: (D)

x₁x₂ + y₁y₂

Answer 2

cos Š P₁OP₂ = $\frac{OP_{1}^{2} + OP_{2}^{2} - (P_{1}P_{2})^{2}}{2(OP_{1})(OP_{2})}$

(OP₁) (OP₂) cos ŠP₁OP₂

x₁x₂ + y₁ y₂