Circumference

Formula for Circumference?

Well - if you eat a pie a day, you will get a big circumference. (Distance around your middle.)

 

C = ∏   x  D    (diameter)

Find the diameter (or double the radius if the radius is given), multiply by pi and you will get the circumference.












Work Smart, Not Hard!

Congruent! Gruesome! Grew Some!

Teacher: "Chris, use the word 'gruesome' in a sentence."
Chris: "A prisoner didn't shave for a week and grew some whiskers."

 

What's this got to do with congruency?

"Congruent" - definition: geometric figures of the same shape and the same size

Note: The figures don't have to be facing in the same direction to be congruent. Think of it as...

"If I cut one shape out, I can rotate it, place it over the top of another shape  and the two shapes will match up exactly."

What if our prisoner above (our con) had a twin brothers who also grew some whiskers....

 

 

Even though con #2 is facing in another direction, he and con #1 are, indeed, congruent.

Work the numbers, not the pictures

When asked for the measure of angle x...

How many people are tempted to...

  a)...              

                        o

...answer   120   ? (Because "x" looks to be twice as big as 60)

       or          

                b)...

...get out a protractor and measure. (And, of course, find that the answer is not one of the 5 choices given.)

                            o

The answer is 30  . The little box at the bottom left                                                                       o

indicates that the two black lines form a 90   angle. 90 - 60 = 30.

The picture is drawn purposely to mislead you. Work the numbers, not the picture.

Some important things to remember are...

All straight lines are 180 degrees.

All interior angles of a triangle add up to 180 degrees.

All interior angles of squares and rectangles add up to 360 degrees.

Up in the Sky! It's a "Y"

Which is the "x" axis and which is the "y"?

1) Well, "y" is the sky, so it is the vertical axis.

2) A pirate ship is sailing ACROSS the ocean to look for treasure. The captain sees an island on the horizon."X" marks the spot on the treasure map. "X" is the horizontal axis.

Complementary? Supplementary?

My students often can't remember which angles are complementary and which ones are supplementary. I always tell them to think of a really cheap wedding, where the complementary (free) drinks are limited to 90. Complementary angles add up to 90 degrees. "C" for "cheap" and "c" for complementary. A "superb" wedding (supplementary) would offer 180 free drinks. supplementary angles add up to 180 degrees. "S" for "superb" and "s" for supplementary. Failing that, I tell them that "c" comes before "s" in the alphabet and 90 comes before 180.

complementary

supplementaryfrom ClipArt, etc.

Quadrilateral Song

Quadrilateral song!
see here