Posted by **Anique** on Monday, March 14, 2011 at 11:05am.

There are 3 vectors:

p= 7i + 10j

q= 3i + 12j

r= -i +4j

Could you show me how to find the angle PQR. using the scalar product.

- Maths -
**Reiny**, Monday, March 14, 2011 at 1:58pm
I will associate your vectors to have endpoints

P(7,10), Q(3,12) and R(-1,4)

then vector(PQ) = (-4,2)

vector(QR) = (-4,-8)

then PQ.QR = |PQ||QR|cos(theta), where theta is the angle between them

16-16 = |PQ||QR|cos(theta)

cos(theta) = 0

theta = 90 degrees

(notice the slope of lines PQ and QR are negative reciprocals of each other, so PQ and QR are perpendicular)

## Answer This Question

## Related Questions

- Physics - Find the scalar product of the vectors ai+bj and bi-aj . Where a and b...
- Math - vectors - For what value of t are these two vectors parallel? a) r = 4i...
- UNIVERSITY PHYSICS 1 - find the magnitude of vectors A=?+4j+4k B=?+2j+3K if the ...
- university physics - find the magnitude of vectors A=?+4j+4k B=?+2j+3k if angle ...
- UNIVERSITY PHYSICS 1 - Find the magnitude of vectors A=?+4j+4k B=?+2j+3k if ...
- Math: Vectors - I forgot how to do the following, so I'm not sure if they're ...
- Physics (vectors) - Given vectors A= (Axi + Ayj), B= (Byj+Bzk) and C= (Cyj + Czk...
- physics - The magnitude of the scalar product of vectors A and B is three times ...
- Physics - Using the definition of the scalar product, find the angles between ...
- AP Physics - Find the scalar product of the vectors in Figure P7.8, where è = ...

More Related Questions