(−a+b)(b–a) Please help I don't understand how to do this

a^2 -2ab + b^2

Step-by-step explanation:

(−a+b)(b–a)

FOIL

first : -a*b = -ab

outer: -a * -a = a^2

inner +b * +b = b^2

last: b* -a = -ab

Add  them together

-ab+a^2 + b^2 -ab

Combine like terms

a^2 -2ab + b^2

a^2+b^2-2ab

Step-by-step explanation:

(-a+b)(b-a)=

first mutiply -a(b-a)=-ab+a^2

second multiply b(b-a)=b^2-ab

then add : -ab+a^2+b^2-ab= a^2+b^2-2ab

4th option is correct xy=-10

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step-by-step explanation: