Asked by Laura

Of the infinitely many lines that are tangent to the curve
y = −7 sin x
and pass through the origin, there is one that has the largest slope. Use Newton's method to find the slope of that line correct to six decimal places.

Answers

Answered by Steve
The slope at any point is

y' = -7cosx

The line through (0,0) and (x,-7sinx) has slope -7sinx/x. That means we need

-7sinx/x = -7cosx
x = tanx

Solutions are
x = 4.493409, 7.725252, 10.904122, ...
The slopes of the lines are
1.521, -0.899, 0.639

See the first couple of lines at

http://www.wolframalpha.com/input/?i=plot+y+%3D+-7sin%28x%29%2C+y%3D1.521x%2C+y%3D-0.899x%2C+from+0+to+15
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