given:E is the midpoint of DF^_. Prove:2DE=DF. D•—-E•—-•F. finish the sentence, It is a give. that E is the midpoint of DF^_. So, DE^_ ~= (blank) by the definition of midpoint. Therefore, DE =EF by the (blank) . DE+EF = DF by the (blank) and so DE+DE = (blank) by substitution . simplifying gives 2DE =DF. FILL IN THE BLANKS USING , -segment congruence postulate - segment addition postulate. -DF^_. -EF^_. - DF. - DE