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JAMB Mathematics 1978 Question 46

Question 46

Vectors and Transformations

The vectors a and b are given in terms of two perpendicular unit vectors i and j on a plane by a = 2i − 3j, b = −i + 2j. Find the magnitude of the vector a + 3b

  1. A.2
  2. B.4
  3. C.√13
  4. D.2√2
  5. E.√10.
Show the answer and explanation

Answer: E (√10.)

Explanation

a + 3b = (2 − 3)i + (−3 + 6)j = −i + 3j, whose magnitude is √(1 + 9) = √10.