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# C4 question Watch

1. Stuck on question 7. I've differentiated it, made it equal to zero,but no clue how to find the coordinates.

For dy /dx I got -4x-y /x +2y I don't understand how to get two values making it zero unless I got the equation wrong.
2. (Original post by eggfriedrice)
Stuck on question 7. I've differentiated it, made it equal to zero,but no clue how to find the coordinates.

For dy /dx I got -4x-y /x +2y I don't understand how to get two values making it zero unless I got the equation wrong.
Substitute into the equation of the curve

There are infinitely many solutions to y=-4x, but you have 2 constraints on x and y.
3. use the fact that the numerator has to be equal to zero (not the denom) - solve for y=, then put back into the implicit equation, solve for x, then put each value of x back into the equation numerator, solve for y=
4. Thanks! Got it.

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