Hello there!
This triangle is an isosceles triangle. Why? Because when we look at a triangle then we see they put the two little slash, it means that it is an isosceles triangle.
How do we find the missing angles?
The rules says that when we have an isosceles triangle, when we add all the angles together, we should find 180 degree.
We have one angle only, which is 40. What two other numbers we can add to 40 to give us 180.
Well, all we have to do is follow the rules.
They say we need to add all the angles together.
40 + x + x = 180
40 + 2x = 180
2x = 180 - 40
2x = 140
x = 140/2
x = 70
The correct answer is 70.
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Justify my work:
40 + 70 + 70 = 180
40 + 140 = 180
180 = 180
I hope this helps!