Class summary 04/02/09 9A

Today we began the class by correcting the Homework. After that we Solved some of the Ex. on the board. #28, #30 and #32 were the ones people had most problems with.

#28.

You were asked to scale factor of ABCD toAEFG.

To do that you need to look at the Figure to the right and then do cross multiply of all the sides and then u'll gett the answer really fast and easy.

As you probably know you can Not have a Fraction with a decimal, so you need to multiply by 10 and and then you have the answer: 8:5. answ.:A.7,5 B.22,4 C.108 D.12,5

#30

Look at the same figure as in the ex. before.

I this one you were asked to find the perimeter of ABCD and AEFG. That is easy to do, since you already counted how long all the side are in ex.#29. so just add all the sides.

And C in #30, is really easy since we have the answer from ex. 29 already. The ratio is 8:5!

#32.

32 was a quite tricky question. In A, they said that all coordinates increased by 2. so u ADD by 2, and that does Not mean that the figure is simliar to the other, its just moves, tha size is still the same.

But if u Multiply by a number, the shape is gonna be bigger. So there is a big different there, and ms.Saatkamp asked us to do that for tomorrow again. be careful there.

After going over the homework we started our lesson for today, Similar angles.

We looked at some postulates and Theorems.

Postulate7-1: AA similarity.

" if two angles of one triangle are congruent to two angles of another triangle, then the triangles are similar"

look at the pict.---->

Theorem 7-1: SSS similarity

" if the measures of the corresponding sides of two triangles are proportional, then the triangles are similar"

Theorem 7-2: SAS similarity

" if the measures of two sides of a triangle are proportional to the measures of two corresponding sides of another triangle and the included angles are congruent, then the triangles are similar."

Theorem 7-3.

"similariti of triangles is Reflexive,symmetric and trensitive"

If you don't remember what they means, here is a review;

Reflexive: Triangle ABC is similar to Triangle ABC

Symmetric:Tr. ABC is similar to Tr. DEF, then Tr.DEF is similar to Tr.ABC

Transitive: Tr.ABC is similar to Tr. DEF and Tr.DEF is similar to Tr.GHI

then Tr.ABC is similar to Tr.GHI

After that we did an ex. about what is going to be on our Homework for tomorrow.

We were supposed to show that CB is 4!

So, just set it up and do the cross multiply.



The easiest thing is to sepatare the Triangles into Two Triangles, one big and one small.






So, u'll get 6CB=24
and the u divide and you'll get the answer 4!

HMWK: Page 358. # 13-18 and #21-25. and don't forget to do nr 30 again!
Good Luck!
Kisses<3