1) (4a - 5b)^2
2) (9x + 3z)^2
3) [ ] (m - n)^2
1) (4a^2+2×4a×(-5b)-5b^2) = (4a+5b)(4a-5b)= (4a-5b)^2
2) (9x^2+2×9x×3z+3z^2) = (9x+3z)(9x+3z)= (9x+3z)^2
3) (m+n)(m-n)= (m-n)^2
4)(x^2 - 18x + 81)=
x^2 - 9x - 9x + 81
x (x - 9) -9 (x - 9)
(x - 9) (x - 9)
(x - 9)^2
