(5x-4)(5x+4)-(2x-3)^2= ?

Răspuns :

(5 x - 4 ) ( 5 x + 4 ) - ( 2 x - 3 )²
= 25 x
² - 20 x + 20 x - 16 - ( 4 x² - 12 x + 9 ) =
= 25 x² - 16 - 4 x² + 12 x - 9 =
=  21 x² + 12 x - 25 
 ... = (5x)² - (4)² - (4x²-12x+9) =
     = 25x² - 16  - 4x² + 12x - 9 =
     = 21x² + 12x - 25