ACT Preparation / Unit 13 ACT 1210 short lesson, about 20 seconds
The Isosceles Triangle
Captions available
The idea
In an isosceles triangle, the angles opposite the equal sides, the base angles, are equal. Conversely, two equal angles mean the sides opposite them are equal.
In practice
An isosceles triangle with a 40° top angle has base angles of 70° each.
Where people slip
Find the equal sides first; the base angles sit opposite them, not between them.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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