√128cos²3π/8-√32=8√2*(1+cos3π/4)/2-4√2=4√2*(1-cosπ/4)-4√2=
=4√2-4√2*1/√2-4√2=-4
(138-38)(138+38)/(122-78)(122+78)=100×176/44×200=176/4400=0.04
=a^6/a^8 =a^(6-8) =a^(-2) =1/a² =1/(2)² =1/4 =0.25
8-y^2
2 ((2^2-y^2))
2((2+y)(2-y))
3x^3y^3-xy+4xy^2-3x^3y^3+2xy+2xy^2=-xy+4xy^2+2xy+2xy^2=xy+4xy^2+2xy^2=xy+6xy^2=xy(1+6y)