Page 78 - Math Course 1 (Book 2)

Measurements in Geometry

relative error
B. Find XZ.
is the ratio of the absolute error to the actual XZ is the measure of XZ
measure. The relative error is expressed as a
percent.
E = absolute error = | p – p* |
rel
value of thing measured | p |
Point Y is between X and Z. XZ can be found by
adding XY and YZ.
Key Concept XY + YZ = XZ Betweenness of points

5 1
4 + 2 = XZ Substitution
8 2
Congruent Segments 1
7 = XZ Add.
8
Words Two segments having the same
measure are congruent.
XZ
Answer 1
Symbols ≌ is read is congruent to. is 7 inches long.
8
Red slashes on the f gure also indicate
that segments are congruent.
Model XY ≌ PQ C. Find x and ST if T is between S and U, ST = 7x,
SU = 45, and TU = 5x – 3.
Y P

X Q
ST + TU = SU

7x + 5x – 3 = 45 Substitute known values.
Let’s Begin 7x + 5x – 3 + 3 = 45 + 3 Add 3 to each side.

12x = 48 Simplify.
12x 48
= Divide each side by 12.
Find Measurements 12 12
x = 4 Simplify.
Examples ST = 7x Given
= 7(4) x = 4
= 28 Multiply.
A. Find LM.
LM is the measure of LM
Answer x = 4, ST = 28

LM + MN = LN Betweenness of points
LM + 2.6 = 4 Substitution
Subtract 2.6 from each
LM + 2.6 – 2.6 = 4 – 2.6
side.
LM = 1.4 Simplify.

LM
Answer
is 1.4 centimeters long.

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