hi people, my question is: find the gradient of the curve

a) at the point where the curve crosses the y axis

and

b) at each of the points wherethe curve crosses the x axis

for a) i differentiated (i think thats what you call what i did) like this:

then made x = 0 as would be the case with the y axis and came up with - 2 which i know is right

but for b) i made y = 0 and used the quadratic formula for x.

and came up with x = 6 or x = -4

the answer for b) written in my textbook is -10, 10

can someone show me how i'v gone wrong please?

thankyou