X^2-7x+7y-y^2
Factor (pls explain)

x(x-7)+y(7-y).

X and Y are common factors so you can factor both out and get this.

δabc ≅ δdcb by sas because

db ≅ ac . . given (side)

bc ≅ bc . . reflexive property (side)

∠dbc ≅ ∠ acb . . alternate interior angles where transversal bc crosses parallel lines bd and ac (included angle)