Answer:
option C
[tex]20\°[/tex]
Step-by-step explanation:
we know that
An isosceles triangle has two equal angles and two equal sides. The two equal angles are the base angles and the third angle is the vertex angle
In this problem the base angles are angle B and angle C
so
m∠B=m∠C
substitute
[tex](5x+5)\°=(7x-25)\°[/tex]
[tex](7x-5x)\°=(5+25)\°[/tex]
[tex]2x=30\°[/tex]
[tex]x=15\°[/tex]
m∠B=[tex](5x+5)\°=5*15+5=80\°[/tex]
Remember that the sum of the internal angles of the triangle is equal to [tex]180\°[/tex]
Find m∠A
m∠A=[tex]180\°-2*80\°=20\°[/tex]
