# Math

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If a = 3i + 2j - k and b = -2i + j calculate each magnitude.

a) a + b
I got sqrt3, but the answer at the back of the book says sqrt11.

2) If D(3,4,5) and E(-2,1,5) are points in space calculate each expression and state what it represents.
|OD|

can you please do those and explain steps.

• Math -

a + b = (3-2) i +(2+1) j +(-1+0) k
= 1 i + 3 j -1 k
sqrt (1^1 + 3^2 + (-1)^2 )
sqrt ( 1 + 9 + 1)
sqrt (11)
The book wins again :)

• Math -

Wow I accidentally put a - in front of 2 and ended up with -1. Thanks!

• Math -

2) If D(3,4,5) and E(-2,1,5) are points in space calculate each expression and state what it represents.
|OD|
-------------------
I assume 0 is the origin (0,0,0)
so OD = (3-0)i + (4-0) j + (5-0) k
and
|OD| = sqrt (3^2 + 4^2 + 5^2)
=sqrt (9 + 16 + 25)
= sqrt(50)
= 5 sqrt(2)

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