(8x-1)(8x+1)-(16x-3)(4x+1)=64x^2-1-(64x^2+16x-12x-3)=<span>64x^2-1-64x^2-16x+12x+3=28x+2</span><span>
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<span>(9xy-3x)-(5xy-x)=9ху-3х-5ху+х=4ху-2х.</span>
a)D(x)={1;2;...;31}
b)f(3)=суббота
f(11)=воскресенье
f(20)=вторник
f(28)=среда
c)S(вторник)=6+13+20+27=66
S(пятница)=2+9+16+23+30=80