http://www.ck12.org Chapter 7. Similarity
1. 142 = 355
2.^355 =^142
3.^52 =^3514
If you cross-multiply all four of these proportions, you would get 70=70 for each one.
Watch this video for help with the Examples above.
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/52555CK-12 Foundation: Chapter7ProportionPropertiesB
Concept Problem Revisited
The scale model of a python is 0.75 ft long and in the ratio 1:24. Ifxis the length of the real python in ft:
1
24
=
0. 75
x
−→x= 24 ( 0. 75 )
x= 18The real python is 18 ft long.
Vocabulary
Aratiois a way to compare two numbers. Ratios can be written in three ways:ab,a:b, andatob. Aproportion
is two ratios that are set equal to each other. To solve a proportion you shouldcross-multiply,which means to set
the product of the numerator of the first fraction and the denominator of the second fraction equal to the product of
the denominator of the first fraction and the numerator of the second fraction. Acorollaryis a theorem that follows
directly from another theorem.
Guided Practice
- In the picture,XYAB=Y ZBC=X ZAC.
Find the measures ofACandXY.