(2-5a)^2=(2-5a)(2-5a)=4-10a-10a+25a^2=25a^2-20a+4
(4b-5a)^2=(4b-5a)(4b-5a)=16b^2-20ab-20ab+25a^2=25a^2+16b^2-40ab
(1/3 x^2-x)^2=(1/3x^2-x)(1/3x^2-x)=1/9x^2 - 1/3x -1/3 x^3 +x^2= 1 1/9x^2-1/3x^3-1/3x
5a-(3a-1)^2=5a-(3a-1)(3a-1)=5a-(9a^2-6a+1)=5a-9a^2+6a-1=-9a^2+11a-1
2y+(4y-5)^2=2y+(4y-5)(4y-5)=2y+16y^2-20y-20y+25=16y^2-38y+25
9a-(4a-5)^2=9a-(4a-5)(4a-5)=9a-(16a^2-20a-20a+25)=9a-16a^2+40a-25=-16a^2+49a-25
(x-2)(x-3)-(x-1)^2=x^2-3x-2x+6-(x^2-x-x+1)=x^2-5x+6-x^2+2x-6=-3x