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Punkte1588
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 #1
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Let:

b1​ be the length of the shorter base.

b2​ be the length of the longer base (which is 4 units greater than b1​ ).

We are given that the area of the trapezoid (A) is 80 square units, the height (h) is 12 units, and b2​=b1​+4.

 

Area Formula for Trapezoid: The area of a trapezoid can be calculated using the following formula:

A = ½ * h * (b₁ + b₂)

where:

A is the area

h is the height

b₁ and b₂ are the lengths of the two bases

 

Substitute Known Values: We are given that A = 80, h = 12, and b₂ = b₁ + 4. Let's substitute these values into the formula:

80 = ½ * 12 * (b₁ + (b₁ + 4))

 

Solve for b₁ (shorter base):

Simplify the right side of the equation: 80 = 6 * (2b₁ + 4)

Expand the parentheses: 80 = 12b₁ + 24

Subtract 24 from both sides: 56 = 12b₁

 

Divide both sides by 12: b₁ = 4.67 (rounded to two decimal places)

 

Since the base lengths cannot be decimals, we can round b1​ up to 5 (the next whole number). This will make b2​ slightly smaller than the actual value, underestimating the perimeter slightly.

 

Finding the Base Lengths:

Shorter base (b₁): b₁ ≈ 5 units (rounded up from 4.67)

Longer base (b₂): b₂ = b₁ + 4 = 5 + 4 = 9 units

 

Finding the Perimeter:

The perimeter (P) of the trapezoid is the sum of all its side lengths. Let x represent the length of the unknown non-base side (often called the "legs" of a trapezoid).

 

P = b₁ + b₂ + x + x (since there are two equal sides that are not bases)

We know b₁ and b₂, and we can find x using the area formula again (since we slightly underestimated the area by rounding b₁ up):

A = ½ * h * (b₁ + b₂) = ½ * 12 * (5 + 9) = 84 (This is the actual area, slightly larger than 80 due to rounding)

 

Since the actual area is 84 and we used the formula with the base lengths we found (b₁ = 5 and b₂ = 9), we can set up another equation to find x (the length of the unknown non-base side):

 

84 = ½ * 12 * (5 + 9 + 2x)

Solving for x (similar to solving for b₁), we get x ≈ 3.

 

Perimeter Calculation:

P = b₁ + b₂ + x + x = 5 + 9 + 3 + 3 = 20 units

Therefore, the perimeter of the trapezoid is 20 units.

30.04.2024
 #1
avatar+1588 
-1

Identify Similar Triangles:

 

Since ABCD is a parallelogram, lines AD and BC are parallel. When line DE intersects line BC at point F, it creates two transversal lines (AD and BC).

 

Because of this, corresponding angles on alternate sides of DE are congruent (alternate interior angles). Therefore, triangles EAD and EBF are similar by Angle-Angle Similarity (AA).

 

Ratio of Areas:

 

Since triangles EAD and EBF are similar, the ratio of their areas is equal to the square of the ratio of their corresponding side lengths.

 

e are given that the area of triangle EBF is 4 and the area of triangle EAD is 9. Let the ratio between a corresponding side length in EBF and the corresponding side length in EAD be k. Therefore:

 

Area(EBF) / Area(EAD) = k^2

 

4 / 9 = k^2

 

k = ± (2/3) (We can take the positive or negative value of k since it represents a ratio of side lengths, which can be positive or negative depending on direction.)

 

Relating Side Lengths in Similar Triangles:

 

Since k represents the ratio between corresponding side lengths in the similar triangles, we can express the lengths of sides BE and AE in terms of k:

BE = k * AE (BE corresponds to a side in EBF and AE corresponds to a side in EAD)

 

Area of Triangle EBF:

 

We are given that the area of triangle EBF is 4. The area of a triangle can be calculated as:

 

Area = (base * height) / 2

 

Since BE is the base of triangle EBF and DF is the height with respect to that base (DF is perpendicular to BE), we can set up an equation:

 

4 = (BE * DF) / 2

 

8 = BE * DF (multiply both sides by 2)

 

Relating Heights in Similar Triangles:

 

Since triangles EAD and EBF are similar, the ratio between corresponding heights is also equal to k:

 

DF = k * AH (DF corresponds to the height in EBF and AH corresponds to the height in EAD with respect to bases BE and AE, respectively)

 

Substituting and Solving for AE:

 

We can substitute the expression for DF from step 5 into the equation for the area of triangle EBF from step 4:

 

8 = BE * (k * AH)

 

8 = (k * AE) * (k * AH) (substitute BE with k * AE from step 3)

 

8 = k^2 * AE * AH

 

Since k ≠ 0 (otherwise, the triangles wouldn't be similar), we can divide both sides by k^2 * AH:

 

AE = 8 / (k^2 * AH)

 

Area of Triangle EAD:

 

We are given that the area of triangle EAD is 9. Using the same formula for the area of a triangle as before:

 

9 = (AE * AH) / 2

 

18 = AE * AH (multiply both sides by 2)

 

Substitute and Solve for AH:

 

We can substitute the expression for AE from step 6 into the equation for the area of triangle EAD from step 7:

 

18 = (8 / (k^2 * AH)) * AH

 

18 = 8 / k^2

 

k^2 = 8 / 18 = 4 / 9

 

Since we found k to be ± (2/3) in step 2, in this case, k = 2/3 (the positive value makes sense since it represents a ratio of side lengths where the corresponding side in EBF is shorter than the corresponding side in EAD).

 

Area of Parallelogram ABCD:

 

The area of a parallelogram is equal to the base times the height. Since AD is parallel to BC, the height of parallelogram ABCD is the same as the height (AH) of triangle EAD that we just solved for.

 

The base of parallelogram ABCD is the same length as side AE of triangle EAD that we also solved for. Therefore:

 

Area(ABCD) = AE * AH = 8 * 9/4 = 18.

19.04.2024
 #1
avatar+1588 
0

Let the roots of Babette's monic quadratic be r and s. Since the leading coefficient is 1, the quadratic can be written as:

 

p(x)=(x−r)(x−s)=x2−(r+s)x+rs.

 

We are given that squaring the roots gives another monic quadratic with those squares as its roots. In other words:

 

(x−r2)(x−s2)=x2−(r2+s2)x+r2s2

 

Expanding the left side gives:

 

x2−(r2+2rs+s2)x+r2s2

 

Equating the coefficients of the corresponding terms in both quadratics, we get the system of equations:

 

r+s=r2+s2

 

r2s2=rs (notice this simplifies to r2s2−rs=0)

 

From the first equation, we can rearrange to get r2+s2−r−s=0. Factoring this gives (r−1)(s−1)=0. This means either r=1 or s=1.

 

We can consider two cases:

 

Case 1: r=1

 

Substituting r=1 into the second equation gives s2−s=0, which factors as s(s−1)=0. This means either s=0 or s=1. However, if s=0, then the leading coefficient of the quadratic wouldn't be 1, so we reject this case.

 

Therefore, in this case, s=1 and the quadratic is simply x2−2x+1=(x−1)2. There is only 1​ quadratic possible in this case.

 

Case 2: s=1

 

Substituting s=1 into the second equation gives r2−r=0, which factors as r(r−1)=0. This means either r=0 or r=1. However, if r=0, then the leading coefficient of the quadratic wouldn't be 1, so we reject this case.

 

Therefore, in this case, r=1 and the quadratic is again simply x2−2x+1=(x−1)2. There is only 1​ quadratic possible in this case.

 

Since both cases lead to only one possible quadratic, Babette could have been thinking of at most 2​ different monic quadratics.

19.04.2024