x的4次方加64乘以y的4次方=x^4+16x^2y^2+64y^4-16x^2y^2=(x²+8y²)²-16x²y²=(x²+8y²+4xy)(x²+8y²-4xy)
x^4+64y^4=(x^2)^2+(8y^2)^2+16(xy)^2-16(xy)^2=[x^2+8y^2]^2-16(xy)^2=(x^2+8y^2-4xy)(x^2+8y^2+4xy)
