estimate difference between 39,875 and 21,158 by rounding to the nearest thousandth before subtracting

Triangle ABD is similar to triangle ABC. The Angle-Side-Angle postulate angle  will apply in this case as the angle ABD is equal to angle ACD and the side AB is common to both triangles and finally we can also see that the angle BAC is also common to both triangles.

Step-by-step explanation:

        Statements                                                    Reasons

∠ABD = ∠ACB                                                GivenSide AB is equal to side AB                       side AB is congruent to side AB                                                                                                                                                            ∠BAC = ∠BAD                                                GivenTriangle ABD is similar to triangle ABC      ASA postulate