Question 4.4.3: Decide whether the following proportions are true. (a) 3/5 =......

(a) Find each cross product.

   \frac{3}{5} = \frac{12}{20}

3 × 20 ≟ 5 × 12

                                             60 = 60

     Since the cross products are equal, the proportion is true.

(b) Find the cross products.

    \frac{2}{3} = \frac{9}{16}

                                        2 × 16 ≟ 3 × 9

                                               32 ≠ 27     Not equal.

This proportion is false, so \frac{2}{3}\ \mathbf{≠}\ \frac{9}{16}.