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In triangle ΔDEF,D=87 and F=43. If ΔDEFΔBAC, then find the measure of A.

Answer
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Hint: In this question we have been given with two triangles which are ΔDEF and ΔBAC, we have given with the measure of two angles from triangle ΔDEF which are D=87 and F=43. Now since we have been given with two angles in the given triangle, we will use the property of triangle which states that the sum of all the angles in a triangle is 180. Using this property, we will find the value of E. And since we have been given that the two triangles are congruent, we will use the property of congruent triangles to get the value of A and get the required solution.

Complete step by step solution:
We know that in ΔDEF,D=87 and F=43.
Now we know that the sum of all the angles in a triangle is equal to 180.
This means that the sum of D,E and F will be 180.
Mathematically, we can write it as:
D+E+F=180
On substituting the values of D=87 and F=43, we get:
87+E+43=180
On adding the angles in the left-hand side, we get:
E+130=180
On transferring the term 130 from the left-hand side to the right-hand side, we get:
E=180130
On simplifying, we get:
E=50
Therefore, we have ΔDEF as follows:
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Now we know that triangles ΔDEFΔBAC, now since both the triangles are congruent, the corresponding angles of the triangle are equal. Therefore, we can create triangle ΔBAC with the same angles as follows:
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Now from the diagram, we can see that A=50, which is the required solution.

Note: It is to be noted that the length of the sides of the two triangles also have the same lengths because congruency in triangles implies that all the corresponding sides and the angles of the triangle are equal. Since we have congruence as ΔDEFΔBAC, we have E=A since they are both the middle angles.



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