An isosceles triangle has two equal sides and two equal base angles. An equilateral triangle has three equal sides and three 60° angles. If two sides are equal, mark the two angles across from them equal. Triangle questions more broadly are in triangle problems.
Use the base angles
If the vertex angle of an isosceles triangle is 40°, each base angle is 70°. Angles in a triangle still add to 180°. An equilateral is the special case where every angle is 60°. Similar triangles, which can also be isosceles, are in similar triangles.
A 45-45-90 triangle is isosceles and right. Use the special-right ratios, in special right triangles. Angle facts around the figure are in lines and angles.
The bottom line
Equal sides, equal opposite angles. Equilateral means 60, 60, 60 and you can stop measuring.
Start practicing
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