Question 839121
2 points are chosen on the parabola defined by y=x^2, one with a positive x-coordinate and the other with a negative x-coordinate. If the points are (a,b) and (c,d), where a < 0 and c > 0, find the y-intercept of the line joining the 2 points in terms of a and c
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Points: 
(a,b) implies b = a^2 because y = x^2
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(c,d) implies d = c^2 because y = x^2
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Using the two points (a,b) and (c,d)
slope = (d-b)(c-a)
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Substituting for b and d you get: 

= (c^2-a^2)/(c-a) = c+a
That is the slope.
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Form of the line: y = mx + k where k is the y-intercept.
a^2 = (c+a)(a) + k
a^2 = ca+a^2 = k
k = -ca (that is the y-intercept)
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Cheers,
Stan H.
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