Head First 2D Geometry

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finding missing angles

Work out what you need to know

Based on your sketch, you need to work out what your theory actually

means in terms of points, lines, and angles.

In this case we’ve got a few important details. We have a line from the

point where Charlie was standing, through the hole in the window, until

it hits the parked car. We also sketched a line moving backward from the

bullet, until that hits the parked car, too.

If our theory is true, and Charlie was the shooter, the way the bullet

bounced off the car is important.

You guys have a bouncing bullet? Cool! Well,

whenever we do lab tests on this type of

bullet they always bounce out at the same

angle as they bounced in on. Does that help?

If our bullet bounced as the lab technician

described, what do we know should be

true about mystery angles x and y?

TIRE

TRACKS

x and y are supplementary

x is less than y

x is equal to y

nothing—they could be any angles

xº

yº

The bullet bounced equally

like this…

…not like this.

bounce

bounce

It’s always worth making

sure the lab technicians

have enough coffee.

Handy lab guy