81х^²-(9х+2у)^²как решить?

Question

81х^²-(9х+2у)^²как решить?

Answer 1

81х^2-(9x+12y)^2 = (9x-9x-12y)*(9x+9x+12y) = -12y(18x+12y) = -216xy-144y

Answer 2

81x^2-(81x^2+36xy+4y^2)=81x^2-81x^2-36xy-4y^2=-36xy-4y^2=-y(36x+4y)