- #1
lemon
- 200
- 0
1. Three points P, Q and R have position vectors p, q and r respectively, where:
p=8i+11j, q=7i-5j and r=2i+4j.
Write down the vectors QP and QR and show that they are not perpendicular. Hence determine the angle PQR.
2. |QP|.|QR|cos(theta)
3. QP= QO+OP=i+16j
QR=QO+OR=-5i+9j
|QP|=root257
|QR|=root106
If the vectors are not perpendicular then a.b=0
a.b= QP=i+16j x QR=-5i+9j = (1)(-5)+(16)(9)=-5+144=139 - not perpendicular
a.b=|QP|.|QR|cos(theta)
cos(theta)=a.b/|QP|.|QR|=139/root257 x root106 = 32.6
Could anybody check to see how pathetic this attempt is, please?
p=8i+11j, q=7i-5j and r=2i+4j.
Write down the vectors QP and QR and show that they are not perpendicular. Hence determine the angle PQR.
2. |QP|.|QR|cos(theta)
3. QP= QO+OP=i+16j
QR=QO+OR=-5i+9j
|QP|=root257
|QR|=root106
If the vectors are not perpendicular then a.b=0
a.b= QP=i+16j x QR=-5i+9j = (1)(-5)+(16)(9)=-5+144=139 - not perpendicular
a.b=|QP|.|QR|cos(theta)
cos(theta)=a.b/|QP|.|QR|=139/root257 x root106 = 32.6
Could anybody check to see how pathetic this attempt is, please?