5) (28+72)^2>28^2 +72^2
7) (x+2)^2 -(x-3)^2=1
x^2+4x+4-x^2+6x-9=1
10x=6
x=6/10
x=0,6
8)4a^2-4b^2-4a+1= (4a^2-4a+1)-4b^2= (2a-1)^2-4b^2=(2a-1-2b)(2a-1+2b)=(2a-2b-1)(2a+2b-1)
б) 16(x-y)^2-25(x+y)^2=(4(x-y)+5(x+y))(4(x-y)-5(x+y))=(4x-4y+5x+5y)(4x-4y-5x-5y)= (9x+y)(-x-9y) = -(9x+y)(x+9y)