Browsing as Guest. Progress, bookmarks and attempts are disabled.
Log in to track your work.
June 2019 p11 q2
318
The line \(4y = x + c\), where \(c\) is a constant, is a tangent to the curve \(y^2 = x + 3\) at the point \(P\) on the curve.
(i) Find the value of \(c\).
(ii) Find the coordinates of \(P\).
Solution
(i) To find the value of \(c\), we need the line \(4y = x + c\) to be tangent to the curve \(y^2 = x + 3\). Substitute \(x = 4y - c\) into the curve equation:
\(y^2 = 4y - c + 3\)
\(y^2 - 4y + c - 3 = 0\)
This is a quadratic in \(y\). For the line to be tangent, the discriminant must be zero:
\(b^2 - 4ac = 0\)
Here, \(a = 1\), \(b = -4\), \(c = c - 3\). So:
\((-4)^2 - 4(1)(c - 3) = 0\)
\(16 - 4c + 12 = 0\)
\(28 - 4c = 0\)
\(4c = 28\)
\(c = 7\)
(ii) With \(c = 7\), substitute back to find \(P\):