Respuesta :

oscar236

Answer:

(x - y + 3)(x + y - 7)

Step-by-step explanation:

x^2 - 4x - 21 + 10y - y^2

= x^2 - y^2 - 4x -21 + 10y

= (x - y)(x + y) - 4x + 10y - 21     Now -21 = + 3 * -7   and +3x - 7x =- 4x so we try:

= (x - y + 3)(x + y - 7)

- this expands to the original expression.

Answer:

(x+y-7)(x-y+3) is your answer

Step-by-step explanation:

x²-4x-21+10y-y²

x²-4x+2²-2²-21+10y-y²

(x-2)²-(y2-10y+25)

(x-2)²-(y-5)²

(x-2+y-5)+x-2-y+5)

(x+y-7)(x-y+3)