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Vectors and 3D Geometry

Vectors, Dot Product

jee_main_2026_april_2_shift_1

Grade 12

Question:

The angle between the vectors a = i + j and b = i - j is:

A. 0°

B. 45°

C. 90°

D. 180°

Step-by-Step Solution

Key Concept: Use the dot product formula: cos θ = (a·b)/(|a||b|).

Step 1: a·b = (1)(1) + (1)(-1) = 0. Step 2: Since dot product is 0, θ = 90°.

Correct Answer: C

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