Math Minute

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Math Minute
Vocabulary
Lesson Presentation
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Math Minute Find the area of the following
figures. 1. A triangle with a base of 12.4 m and
a height of 5 m 2. A parallelogram with a base
of 36 in. and a height of 15 in. 3. A square
with side lengths of 2. yd
31 m2
540 in2
4 yd2
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Learn to find the area of irregular figures.
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You can find the area of an irregular figure by
separating it into non-overlapping familiar
figures. The sum of the areas of these figures is
the area of the irregular figure. You can also
estimate the area of an irregular figure by using
graph paper.
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Example 1 Estimate the area of the figure. Each
square represents one square yard.
Count the number of filled or almost-filled
squares 11 red squares.
Count the number of squares that are about
half-full 8 green squares.
Add the number of filled squares plus ½ the
number of half-filled squares 11 ( 8)
11 4 15.
1 2
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Example 2 Finding the Area of an Irregular
Figure Find the area of the irregular figure. Use
3.14 for p.
9 yd
9 yd
Use the formula for the area of a rectangle.
3 yd
Substitute 8 for l.
Substitute 9 for w.
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Continued Find the area of the irregular figure.
Use 3.14 for p.
9 yd
9 yd
Substitute 2 for b and 9 for h.
2 yd
Multiply.
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Now You Try Find the area of the irregular
figure. Use 3.14 for p.
16 m
9 m
16 m
Use the formula for the area of a parallelogram.
Substitute 16 for b.
Substitute 9 for h.
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Continued Find the area of the irregular figure.
Use 3.14 for p.
16 m
9 m
16 m
Substitute 3.14 for p and 8 for r.
Multiply.
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Additional Example 2 Continued Find the area of
the irregular figure. Use 3.14 for p.
16 m
9 m
16 m
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Continued Find the area of the irregular figure.
Use 3.14 for p.
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Example 3 Finding the Shaded Region Find the
area of the shaded region Use 3.14 for pi.
Step 1 Write the formula.
A area of square area of circle
A (l x w) ( pr2)
4 cm
Step 2 Substitute values.
2 cm
A (4 x 4) (3.14 x 22)
Step 3 Solve.
A (16) (3.14 x 4)
A (16) (12.56)
4 cm
A 3.44 cm2