Question

Expand (3x - y + 4)(3x - y - 7)​

Answer 1

Answer:

$(3x - y + 4)(3x - y - 7) \\ = 3x(3x - y - 7) - y(3x - y - 7) + 4(3x - y - 7) \\ = 9 {x}^{2} - 3xy - 21x - 3xy + {y}^{2} + 7y + 12x - 4y - 21 \\ = 9 {x}^{2} + {y}^{2} - 6xy - 21x + 12x + 7y - 4y - 21 \\ = 9 {x}^{2} + {y}^{2} - 6xy - 9x + 3y - 21$