Consider the tangent to the parabola at (b, b^2). If this tangent is to pass through the point (0, -a^2) then the gradient of the tangent is . But the gradient of the tangent is also .

Equate the two expressions and solve for b (in terms of a).

Knowing the gradient of the tangent and a point lying on the tangent, you shuld be able to write down the equation of the tangent.

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