760.

х² - х - 72 =

= х² + 8х - 9х - 72 =

= (х² - 9х) + (8х - 72) =

= х(х - 9) + 8(х - 9) =

= (х - 9)(х + 8),

762.

3а² + 8а + 5 =

= 3а² + 5а + 3а + 5 =

= (3а² + 3а) + (5а + 5) =

= 3а(а + 1) + 5(а + 1) =

= (а + 1)(3а + 5),

764.

15u² + u - 2 =

= 15u² + 6u - u - 2 =

= (15u² - 5u) + (6u - 2) =

= 5u(3u - 1) + 2(3u - 1) =

= (3u - 1)(5u + 2)