1) 16 - b² = 4² - b² = ( 4 - b ) × ( 4 + b )
2) c² - 49 = c² - 7² = ( c - 7 ) × ( c + 7 )
5) 4x² - 25 = 2²x² - 5² = ( 2x )² - 5² = ( 2x - 5 ) × ( 2x + 5 )
1) 16 - b² = 4² - b² = ( 4 - b ) × ( 4 + b )
2) c² - 49 = c² - 7² = ( c - 7 ) × ( c + 7 )
5) 4x² - 25 = 2²x² - 5² = ( 2x )² - 5² = ( 2x - 5 ) × ( 2x + 5 )