Answer:
55°
Step-by-step explanation:
The definition of an isosceles triangle is that there are two sides of equal length and one side of a different length. Because two sides have the same length, their respective angles have the same measure. For example, side BC goes with angle A; because it is the same length as side AB which goes with angle C, angles A and C are the same. Just set the angles equal to each other and begin solving an algebraic expression as shown here:
[tex]3x+40=x+50\\3x-x+40 = x-x+50\\2x+40=50\\2x+40-40=50-40\\2x=10\\\frac{2x}{2} =\frac{10}{2} \\x=5[/tex]
Now that you know what x is equal to, plug it into angle A's equation.
[tex]3(5)+40\\15+40\\55[/tex]
Angle A is equal to 55°
