Browsing as Guest. Progress, bookmarks and attempts are disabled.
Log in to track your work.
June 2020 p12 q6
313
The equation of a curve is \(y = 2x^2 + kx + k - 1\), where \(k\) is a constant. Given that the line \(y = 2x + 3\) is a tangent to the curve, find the value of \(k\).
Solution
To find the value of \(k\), we set the curve equation equal to the line equation since the line is tangent to the curve:
\(2x^2 + kx + k - 1 = 2x + 3\)
Rearrange to form a quadratic equation:
\(2x^2 + (k-2)x + (k-4) = 0\)
For the line to be tangent to the curve, the discriminant of the quadratic must be zero:
\(b^2 - 4ac = 0\)
Here, \(a = 2\), \(b = k-2\), \(c = k-4\). Substitute these into the discriminant formula: