In isosceles triangles, the angle at the base is 70 degrees to which the other angles are equal.

The angles at the base of an isosceles triangle are equal to each other, since equal lateral sides are adjacent to them. I.e

∟1 = ∟2 = 70o – angles at the base of an isosceles triangle.

Since the total sum of all the angles of the triangle is 180 °, then to find one of the angles, we subtract the sum of equal angles from this sum:

180o – (70o + 70o) = 180o – 140o.

Answer: 40o.

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