Official Guide - p. 262, q. 14 - diagonal of 3-d rectangle

[baily106]

Question 14 on page 262 has a figure that I cannot draw on here. I would like to know how does one find the diagonal (AB) of a rectangular sold when the height is 2, the length is 10 and the width is 7.

Thanks,
Anisha

[tommywallach]

Hey Anisha,

You can actually do Pythagoras in three dimensions. You would think they would've taught this in the lesson, but they don't (silly official guide!):

a ^ 2 + b ^ 2 + c ^ 2 = d ^ 2

7 ^ 2 + 2 ^ 2 + 10 ^ 2 = d ^ 2

49 + 4 + 100 = d ^ 2

153 = d ^ 2

d = rt. 153 = rt. 9 * rt. 17 = 3 rt. 17

Hope that helps!

-t

[baily106]

I didn't not know that; it helps a lot.
Thank you!

[tommywallach]

Glad to help!