Answer:
see the explanation
Step-by-step explanation:
we know that
An isosceles triangle has two equal sides and two equal angles
step 1
Find the measure of angle BDA
we know that
Triangle ABD is an isosceles triangle
AB=AD ---> given problem
so
m∠ABD=m∠BDA
therefore
m∠BDA=72°
step 2
Find the measure of angle BAD
Remember that the sum of the interior angle in a triangle must be equal to 180 degrees
In the triangle BDA
m∠ABD+m∠BDA+m∠BAD=180°
substitute the given values
72°+72°+m∠BAD=180°
144°+m∠BAD=180°
m∠BAD=180°-144°=36°
step 3
Find the measure of angle BCA
In the triangle ABC
m∠BCA=m∠BAC
we have that
m∠BAC=m∠BAD=36°
therefore
m∠BCA=36°
step 4
Find the measure of angle ABC
In the triangle ABC
m∠BAC+m∠BCA+m∠ABC=180°
substitute the given values
36°+36°+m∠ABC=180°
72°+m∠ABC=180°
m∠ABC=180°-72°=108°
step 5
Find the measure of angle DBC
we know that
m∠DBC+m∠ABD=m∠ABC ----> by addition angle postulate
substitute the given values
m∠DBC+72°=108°
m∠DBC=108°-72°=36°
step 6
Find the measure of angle BDC
we know that
m∠BDC+m∠ADB=180° ----> by supplementary angles
substitute the given value
m∠BDC+72°=180°
m∠BDC=180°-72°=108°
step 7
In the triangle DBC we have
m∠DBC=36°
m∠BCD=m∠BCA=36°
so
The triangle BCD has two equal angles
therefore
Triangle BCD is an isosceles triangle
and
BD=BC
