i have 2 questions, the first one i could do, its the second i need help with. 1) determine the coordinates of the centre and the radius of the circle with equation $\displaystyle x^2 + y^2 - 6x + 8y = 0$. so i put it in its squared form (if thats what you call it. if not, any corrections would be appreciated) like so:

$\displaystyle (x - 3)^2 - 9 + (y + 4)^2 - 16 = 0$

$\displaystyle \implies (x - 3)^2 + (y + 4)^2 = 25$ so the centre must be $\displaystyle (3, -4)$ and the radius is 5

the second question which i need help with is:

find the coordinates of the points P and Q, where the line $\displaystyle x = 7$ intersects this circle. could someone show me in detail the way you would answer this

thanks for any help