Astudent made the following chart to prove that ab2 + bc2 = ac2. (see attachment)
which of the first four steps is the error?

Step-by-step explanation:

The first step is wrong.

It's completely wrong because in the first step the student's justification of the congruence doesn't make sense. Basically because angle BCA is not corresponding to angle BCD, the right equivalence would be between angle BCA and DCB.

So, the student is demonstrating wrong the triangles congruence, because he is establishing a congruence between angles that don't correspond, there are in different spots.

Therefore, the first step is the error.

1. 3.4/4

2. 0.8/7

3. 0.5 x 3

4. 0.9 x 6

5. 10.8

6. 2.35

7. 0.567

8. 9.35

9. 0.02

10. 0.06

11. 0.16

12. 0.42

13. 0.63

14. 5.6

15. 8.1

16. 9.9

17. 0.28

18. 0.48

19. 0.27

20. 0.49

21. 0.45

22. 0.72

23. 0.9

24. 0.88

25. 0.75

26. 0.16

27. 0.328

28. 0.495

29. 0.72

30. 1.068

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.