The GATE Grind

GATE 2019 MT – Question 14

Engineering Mathematics · Calculus and vector calculus · 1 mark · Multiple choice

Find the directional derivative of $\phi=x^2+y$ along $\hat u=(3\hat i+4\hat j)/5$ at (1,1).

  1. 3
  2. 2
  3. 1
  4. 0

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) 2

Explanation

The gradient is (2x,1), hence (2,1) at (1,1). Dot it with the specified unit vector: (2×3+1×4)/5=2. Thus B. No further normalization is necessary because u is already a unit vector.

More Calculus and vector calculus questions

All Calculus and vector calculus questions →