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**mark** ok i've used the simplified quadratic formula (because the discriminant is 0) $\displaystyle \frac{5m}{1+ m^2}$ then $\displaystyle \frac{5(4/3)}{1 + (16/9)}$ which came to $\displaystyle \frac {60/9}{25/9}$ and i've arrived at x = 2.4 and y = 3.2. **<<<<<<<<< That means the point A is A(2.4, 3.2)**

**Now use $\displaystyle \color{blue}\bold{m=-\dfrac43}$ to get the coordinates of B(-2.4, 3.2)**

then using the distance formula like so $\displaystyle \sqrt {2.4^2 + 3.2^2}$ which come to $\displaystyle \sqrt {5.76 + 10.24}$ which equals $\displaystyle \sqrt {16}$ which is 4. the answer given to me by the book is 4.8 though? what have i done wrong here?