The tangent to the curve y2 + 2x − 5 = 0 at the point (h, k) is parallel to the line x + 2y = 4, then the value of ‘k’ is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2
Differentiating \(y^2 + 2x - 5 = 0\) with respect to x:
\( \displaystyle 2y\frac{dy}{dx} + 2 = 0 \)
\( \displaystyle \frac{dy}{dx} = -\frac{1}{y} \)
So the slope of the tangent at (h, k) is \(-\frac{1}{k}\).
The line x + 2y = 4 can be written \(y = -\frac{1}{2}x + 2\), so its slope is \(-\frac{1}{2}\).
Parallel lines have equal slopes:
\( \displaystyle -\frac{1}{k} = -\frac{1}{2} \)
\(k = 2\)
The point is on the curve: \(4 + 2h - 5 = 0\) gives \(h = \frac{1}{2}\), so (h, k) = \(\left(\frac{1}{2}, 2\right)\).