Posted by **Anonymous** on Tuesday, December 11, 2012 at 10:18am.

let p=(1,1,1), Q=(2,3 5), and R=(-1,3,1). find the area A of thr triangle with vertices P,Q, and R

- calculas -
**Steve**, Tuesday, December 11, 2012 at 10:32am
get the sides of the triangle, then use Heron's formula:

PQ = √(1^2+2^2+4^2) = √21

QR = √(3^2+0^2+4^2) = 5

RP = √(2^2+2^2+0^2) = √8

I'll let you use Heron's formula. Probably better to convert to decimals rather than having all those nested roots.

- OR - calculus -
**Reiny**, Tuesday, December 11, 2012 at 11:07am
area of triange = (1/2)|vector PQ x vector PR|

vector PQ = [1,2,4] and vector PR = [-2, 2,0}

PQ X PR = [-8,-8,6]

area = (1/2)√(64+64+36) = 1/2 √164

= 1/2 (2√41) = √41

- calculus - duh -
**Steve**, Tuesday, December 11, 2012 at 11:31am
good job, Reiny. Forgot about vectors!

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