f.3數學唔識做

1)2t3-18s2t
= 2t ( t2 – 9s2 )
= 2t ( t + 3s )( t – 3s )
2)16(p+q)2-25q2
= 42 ( p + q )2 – ( 5q )2
= { 4 ( p + q ) + 5q }{ 4 ( p + q ) – 5q }
= ( 4p + 4q + 5q )( 4p + 4q – 5q )
= ( 4p + 9q )( 4p – q )
3)96k2-54h2
= 6 ( 16k2 – 9h2 )
= 6 ( 4k + 3h )( 4k – 3h )
4)75(c-3d)2-27(2c-5d)2
= 3 { 25 ( c – 3d )2 – 9 ( 2c – 5d )2 }
= 3 { 5 ( c – 3d ) + 3 ( 2c – 5d )}{ 5 ( c- 3d ) – 3 ( 2c – 5d )}
= 3 ( 5c – 15d + 6c – 15d )( 5c – 15d – 6c + 15d )
= 3 ( 11c – 30d )( - c )
= - 3c ( 11c – 30d )
= 3c ( 30d – 11c )