`10) x^2 - 9 - 5( x + 3 )`
`= ( x + 3 )( x - 3 ) - 5( x + 3 )`
`= ( x + 3 )( x - 3 - 5 )`
`= ( x + 3 )( x - 8 )`
`11) 5( x - y ) + y^2 - xy`
`= 5( x - y ) - ( xy - y^2 )`
`= 5( x - y ) - y( x - y )`
`= ( 5 - y )( x - y )`
`12) x^2 + 5x - 14`
`= ( x^2 + 7x ) - ( 2x + 14 )`
`= x( x + 7 ) - 2 ( x + 7 )`
`= ( x - 2 )( x + 7 )`