... – b 1 )(a 1 + b 2 )(a 2 + b 2 ) = [(a 1 a 2 – (a 1 + a 2 )b 1 + b 1 2 ][a 1 a 2 +(a 1 + a 2 )b 2 +b 2 2 ] = (1 + pb 1 + b 1 2 ) (1 – pb 2 + b 2 2 ) = (pb 1 –qb 1 )(–qb 2 – pb 2 ) = (p – q)b 1 . ... b 1 , b 2 . Chứng minh : (a 1 – b 1 )(a 2 – b 2 )(a 1 + b 2 )(a 2 + b 2 ) = q 2 – p 2 Giải : Theo định lý Viet ta có : a 1 + a 2 = – p, a 1 a 2 = 1 , b 1 + b 2 = – q , b 1 b 2 = 1 (a 1 – b 1 ... , by , cz ta được : (a + 1) x = ax + by + cz ; (b + 1) y = ax + by + cz ; (c + 1) z = ax + by + cz ⇒ + + + + = + + = = + + + + + + + + + + + 1 1 1 x y z x y z 2 1 a 1 b 1 c ax by cz ax by cz ax...