Question:

Why does a negative time a negative equal a positive? Think of it in terms of action and debt. If a negative number represents a debt, then multiplying by a negative number represents the removal of that debt. (Hint: If someone takes away (-) four of your debts that are each worth ₹ 3 (that is, -3), you are effectively ₹ 12 richer! Therefore, (-3) × (-4) = +12. [Page No. 46]

Answer: Verified

A negative number stands for a debt. Multiplying by a positive number means having that many debts; multiplying by a negative number means taking away that many debts. If four debts of ₹ 3 each (each debt is -3) are removed from you, you lose ₹12 of debt, you are ₹12 richer.
So, $(-3) \times (-4) = +12$ .

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More NCERT Questions

Try to extend this method for constructing line segments of lengths sqrt(3) and sqrt(5) using a ruler and a compass. Generalise this method to construct a line segment of any length of the form sqrt(n Consider this puzzle: What is the square root of -1? We know that 1 × 1 = 1. We also know that (-1) × (-1) = 1. There is no real number that, when multiplied by itself, results in a negative number. T The decimal expansion of p/q will be terminating precisely when the prime factors of q are only 2, only 5, or both 2 and 5. Can you explain why? [Page No. 58] Try to find the decimal expansions of 10/3 and 11/12. What do you observe about the repetition of the digits after the decimal point? [Page No. 57]

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