Question

Multiply the sum of 6 upon 7 and minus 13 upon 21 by their difference

Answer 1

Answer:

$= \frac{6}{7} + \frac{ - 13}{21} \\ \\ = \frac{6 \times 21 + ( - 13 \times 7)}{21 \times 7 } \\ \\ = \frac{126 + ( - 91)}{147} \\ \\ = \frac{126 - 91}{147} \\ \\ = \frac{35}{147} = \frac{5}{21} .....i \\ \\ \\ = \frac{6}{7} - ( \frac{ - 13}{21} ) \\ \\ = \frac{6 \times 21 - ( - 13 \times 7)}{7 \times 21} \\ \\ = \frac{126 - ( - 91)}{147} \\ \\ = \frac{126 + 91}{147} \\ \\ = \frac{225}{147} = \frac{75}{49} .......ii \\ \\ multiply \: i \: and \: ii \\ \\ = \frac{5}{21} \times \frac{75}{49} \\ \\ = \frac{375}{1029} = \frac{125}{343}$