At what point does the normal to y=2+1x+4x2 at (1,7) intersect the parabola a second time?
( __________, ___________ )
(The normal line is perpendicular to the tangent line. If two lines are perpendicular their slopes are negative reciprocals -- i.e. if the slope of the first line is m then the slope of the second line is −1/m)
( __________, ___________ )
(The normal line is perpendicular to the tangent line. If two lines are perpendicular their slopes are negative reciprocals -- i.e. if the slope of the first line is m then the slope of the second line is −1/m)
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y = 4x^2 + x + 2
y ' = 8x + 1 <===
y ' (1) = 8*1 + 1 = 9 <=== slope of tangent
. . . slope of normal = - 1/9
y = mx + b
m = -1/9 ; x = 1 ; y = 7
7 = -1/9 * 1 + b
b = 64/9
y = -1/9 x + 64/9 <=== normal
normal intersects where
-1/9 x + 64/9 = 4x^2 + x + 2
4 x^2 + 10 / 9 x - 46/9 = 0
2/9 (x - 1) (18x + 23) = 0
x = 1 ... or ...
x = - 23/18 <===
y = -1/9 * - 23/18 + 64/9 = 1175 / 162
(-23/18 , 1175/162) <=== second intersection point.
y ' = 8x + 1 <===
y ' (1) = 8*1 + 1 = 9 <=== slope of tangent
. . . slope of normal = - 1/9
y = mx + b
m = -1/9 ; x = 1 ; y = 7
7 = -1/9 * 1 + b
b = 64/9
y = -1/9 x + 64/9 <=== normal
normal intersects where
-1/9 x + 64/9 = 4x^2 + x + 2
4 x^2 + 10 / 9 x - 46/9 = 0
2/9 (x - 1) (18x + 23) = 0
x = 1 ... or ...
x = - 23/18 <===
y = -1/9 * - 23/18 + 64/9 = 1175 / 162
(-23/18 , 1175/162) <=== second intersection point.