1)a²+4²-9c²-4ab x³+x²-xy²-y² 2)(5+2x)²-2.5x(8x+7) при x=-0.5

X^3+x^2-xy^2-y^2=(x^3+x^2)-(xy^2+y^2)=x^2(x+1)-y^2(x+1)=(x^2-y^2) (x+1)
2)5+2*(-0,5)-2,5*(-0,5)*(8*(-0,5)+7)=5-1+1,25*3=4-3,75=7,75
=(a^2-9c^2)-(4^2+4ab)=(a-3c)(a+3c)-4(1+ab)