Answer
$4-y^{10}$
Note that standard form would list the variables first in decreasing order of exponent, so another way to write this answer is: $-y^{10}+4$.
Work Step by Step
$$(2-y^5)(2+y^5)$$ $$=(2\times 2)+(2\times y^5)+(-y^5\times 2)+(-y^5\times y^5)$$ $$=4+2y^5-2y^5-y^{10}$$ $$=4-y^{10}$$
Note that standard form would list the variables first in decreasing order of exponent, so another way to write this answer is: $$-y^{10}+4$$
