Then the vector OQ=(a, b)

a^2+b^2=6^2+8^2= 100

Vector OP OQ=|OP||OQ|cos 135

6a+8b=-50√2

a^2+b^2= 100

A=√2 or -7√2

B=-7√2 or -√2

So the third quadrant of Q (-7√2,-2)