(2m+3)×(2m-3)
(2m)²-3²
4m² -9
(7m+3n)×(7m-3n)
(7m)²-(3n)²
49m² -9n²
(2c-1/2)×(2c+1/2)
(2c)² '(1/2)²
4c²-1/4
(4/5x+y)×(y-4/5x)
-16/25x²+y²
1) (4y -y(2-y)/(2-y) * (y-2)/(y+2) =(4y-2y+y²)*(y-2) / (2-y)*(y+2) =(2y +y²)(y -2) / -(y -2)(y +2) = -y(2 +y) /(y +2) = -y