The measures of the angles of the isosceles triangle are 55, 55 and 70.
Explanation:
An isosceles triangle has two congruent base angles and a vertex angle.
Let
b
=the measure of one of the base angles.
Let
v
=
the measure of the the vertex angle.
The vertex angle is 40 degrees less than the sum of the base angles.
v
=
b
+
b
−
40
=
2
b
−
40
The sum of the measures of the angles of a triangle is 180.
b
+
b
+
v
=
180
Substitute
2
b
−
40
for
v
.
b
+
b
+
2
b
−
40
=
180
4
b
−
40
=
180
+40+40
Combine like terms.
Add 40 to both sides.
4b=220
Divide by 4
4
b/4
=
220
/4
b
=
55
v
=
2
b
−
40
v
=
2
(
55
)
−
40
=
70
