# The Ray Tracer Challenge: p. 28

**URL:** <https://forum.devtalk.com/t/the-ray-tracer-challenge-p-28/9499>\
**Category:** PragProg Customers\
**Tags:** book-the-ray-tracer-challenge, errata\
**Created:** [10 May 2021 21:52 UTC](https://forum.devtalk.com/t/the-ray-tracer-challenge-p-28/9499 "2021-05-10T21:52:42Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![jamis](https://forum.devtalk.com/user_avatar/forum.devtalk.com/jamis/32/1083_2.png) [@jamis](https://forum.devtalk.com/u/jamis)\
**Post date:** [11 May 2021 02:39 UTC](https://forum.devtalk.com/t/the-ray-tracer-challenge-p-28/9499/2 "2021-05-11T02:39:31Z")

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It looks like you might have a typo in your second matrix (“B”). In the second row, the first number is a positive “3”, rather than negative. That should get you the expected answer.

- Jamis

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