The curve \(y = \frac{10}{2x+1} - 2\) intersects the \(x\)-axis at \(A\). The tangent to the curve at \(A\) intersects the \(y\)-axis at \(C\).
(i) Show that the equation of \(AC\) is \(5y + 4x = 8\).
(ii) Find the distance \(AC\).
Solution
(i) To find the equation of the tangent at \(A\), we first find the derivative of the curve:
\(\frac{dy}{dx} = \frac{-10}{(2x+1)^2} \times 2\).
At \(A\), \(y = 0\), so \(x = 2\).
The slope \(m\) at \(x = 2\) is \(\frac{-4}{5}\).
The equation of the tangent is \(y = \frac{-4}{5}(x - 2)\).
Rearranging gives \(5y + 4x = 8\).
(ii) The point \(C\) is \((0, 1.6)\).
The distance \(AC\) is \(\sqrt{(1.6)^2 + 2^2} = 2.56\).
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