randRange( 20, 160 ) shuffle( randFromArray( [ [ 2, 4 ], [ 3, 5 ] ] ) ) KNOWN_INDEX % 2 === 0 ? ANCHOR : 180 - ANCHOR $._("pink angle") $._("green angle")

If we know that the blue angle is MEASURE^\circ, what is the measure of angle x?

MEASURE \Large{^\circ}
init({ range: [[-4, 4], [-1, 1]], scale: 60 }); graph.pl = new ParallelLines(0, 0, 4, 0, 0); graph.pl.draw(); graph.pl.drawTransverse(ANCHOR); graph.pl.drawAngle(KNOWN_INDEX, true); graph.pl.drawAngle(UNKNOWN_INDEX, "x", GREEN);

What is the measure of the pink angle?

graph.pl.drawAngle(KNOWN_INDEX + 1, false, PINK);

The pink and blue angles add up to 180^\circ because they are adjacent and form a straight line.

\pink{\text{PINK_ANGLE}} = 180^{\circ} - \blue{MEASURE^{\circ}} = \green{180 - MEASURE^{\circ}}

graph.pl.drawAngle(KNOWN_INDEX + 1, true, PINK);

The pink and green angles also add up to 180^\circ because they are adjacent and form a straight line too.

\green{\text{GREEN_ANGLE}}= 180^{\circ} - \pink{180 - MEASURE^{\circ}} = \green{MEASURE^{\circ}}

graph.pl.drawAngle(UNKNOWN_INDEX, true, GREEN);