If A has rows (3, 1) and (-2, 0) and B has rows (-2, -1) and (4, -1), find the entry in row 2, column 1 of AB.
Answer and explanation
Correct answer: D.
- Step 1: The entry is (row 2 of A) · (column 1 of B). Step 2. (-2)(-2) + (0)(4) = 4. **Answer: . Why not the others:** is what you get if you multiply the entries by rows of B instead of columns. is what you get if you multiply the matching entries. does not fit.
Practise more Matrices, calculus and coordinate geometry.
Free questions with an explanation for every one, and full timed WBJEE mock tests.
More Matrices, calculus and coordinate geometry questions
- Find the determinant of the 3×3 matrix with rows (-2, 0, 3); (-1, 5, -1); (2, 1, -1).
- If A has rows (3, -3) and (3, -1) and B has rows (-3, 4) and (3, 2), find the entry in row 2, column 1 of AB.
- Find the coordinates of the focus of the parabola y² = 12x.
- Find a × b for a = 3i + 4j − 1k and b = 2i − 2j + 3k.
- Solve dy/dx = 2x with y(0) = -1. What is y(3)?
- How many permutations of 10 objects taken 3 at a time are there?