"A student made the following chart to prove that AB2 + BC2 = AC2.


Statement Justification

  1. Triangle ABC is similar to triangle BDC 1. Angle ABC = Angle BDC and Angle BCA = Angle BCD
  2. BC2 = AC × DC 2. BC ÷ DC = AC ÷ BC because triangle ABC is similar to triangle BDC
  3. Triangle ABC is similar to triangle ABD 3. Angle ABC = Angle BAD and Angle BAC = Angle ABD
  4. AB2 = AC × AD 4. AB ÷ AD = AC ÷ AB because triangle ABC is similar to triangle ABD
  5. AB2 + BC2 = AC × AD + AC × DC

= AC (AD + DC)

  1. Adding Statement 1 and Statement 2
  2. AB2 + BC2 = AC2

Which of the first four steps is the error?"

A student made the following chart to prove that AB2 + BC2 = AC2. Statement Justification 1. Triangle ABC is similar to triangle BDC 1. Angle ABC = Angle BDC an class=

Verified Answer :

Step 3 has an error.

Step-by-step explanation:

Similarity-criteria of triangles:

1. All the corresponding angles of two triangles should be equal.

2. The ratio between the corresponding sides of two triangles should be equal.

In \(\triangle ABC\) and \(\triangle BDC\)  

\(\angle BAC = \angle DBC \\\angle ACB = \angle BCD\)

All the angles of triangle are equal.

∴\(\triangle ABC \sim \triangle BDC\)

Since, \(\triangle ABC \sim \triangle BDC\)

\(\frac{AC}{BC}=\frac{AC}{DC}\)

\(BC^{2}=AC \times DC\)

In \(\triangle ABC\) and \(\triangle BDA\),

\(\fbox{\begin\\ \angle ABC= \angle BDA = 90^{\circ}\end{minispace}}\)

\(\fbox{\begin \\\angle BAC = \angle BAD\\\end{minispace}}\)

\(\angle ACB = \angle ABD\)

All the angles of triangle are equal.

∴\(\fbox{\begin\triangle ABC \sim \triangle BDA \end{minispace}}\)

∵\(\triangle ABC \sim \triangle BDA\)  

\(\frac{AC}{AB}=\frac{AB}{AD}\)

\(AB^{2}=AC \times AD\)

Now, \(AB^{2}+BC^{2}\) can be simplified as,

\(AB^{2}+BC^{2}=AC \times AD+AC \times DC\\AB^{2}+BC^{2}=AC(AD+DC)\\AB^{2}+BC^{2}=AC(AC)\\AB^{2}+BC^{2}=AC^{2}\)

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Answer Details

Grade: Junior High School

Subject: Mathematics

Chapter: Triangle

Keywords: triangle, similar, similarity, ratio of sides, right triangle, similar triangle, ratio of sides, equal angles, square of hypotenuse, sum, square of legs, sum of square of legs

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Answer: its justification 4

i just finished the test and this was right!!!