Answer
False
Work Step by Step
RECALL:
$(a-b)^2 = a^2-2ab+b^2$
Note that $(-x+y) = -(x-y)$
Thus,
$(-x+y)(x-y) = -(x-y)(x-y) = -(x-y)^2$
Use the formula above to obtain:
$-(x-y)^2
\\= -(x^2-2xy+y^2)
\\= -x^2-(-2xy)-y^2
\\=-x^2+2xy-y^2$
Therefore, the given statement is false.