The first formula is 1 / 1 × 3 = 1 / 2-1 / 6, the second formula is 1 / 2 × 4 = 1 / 4-1 / 8, and the third formula is 1 / 3 × 5 = 1 / 6-1 / 10

The first formula is 1 / 1 × 3 = 1 / 2-1 / 6, the second formula is 1 / 2 × 4 = 1 / 4-1 / 8, and the third formula is 1 / 3 × 5 = 1 / 6-1 / 10

The multiplication of the first factor of the first test (the formula before the equal sign) by 1 / 2 is equal to the subtraction of the formula after the equal sign; the multiplication of the second factor of the formula before the equal sign by 2 is equal to the subtraction after the equation; all equations are equal to the multiplication before the equal sign and the subtraction after the equal sign