Pythagorean theoremThe rule that in a right triangle, the squares of the two shorter sides add up to the square of the longest side: a² + b² = c².
You’ll leave with these skills
01Find all four angles where two lines crossCopy the known angle to the angle across from it, and subtract it from 180 degrees for the two angles beside it.
02Find every angle where a line crosses two parallel linesSort the eight angles into small and big ones: all the small ones are equal, and each small one plus a big one makes 180 degrees.
03Tell from a figure’s marks which angle rules applyLook for arrow marks, the word parallel, or a small square in a corner before you set any two angles equal.
04Solve for x in an angle expression and find the angle it givesWrite the equation the angles' relationship gives (equal, adding to 180°, or adding to 90°), solve for x, then plug x back in to get the angle the question asks for.
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