Solve the following:
In an isosceles triangle, the base angles are equal. The vertex angle is 40°. What are the base angles of the triangle? (Remember, the sum of three angles of a triangle is 180°).
Let the base angles be equal to b.
The sum of all interior angles of a triangle is 180°.
b + b + 40° = 180°
2b + 40° = 180°
2b = 180º - 40º = 140º (Transposing 40º to R.H.S.)
Dividing both sides by 2,
`(2b)/2 = 140^@/2`
b = `70^@`
Therefore, the base angles of the triangle are of 70º measure.
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