# Math Help - NEwtons Method

1. ## NEwtons Method

I need help with these two, I don't get it.

1. Use Newton's method to find a zero of the function, f(x)=x^3-3 x+6, using x[0]=-1. Explain why the method fails. Fix it so that it does find a zero.

2. In the figure, the length of the chord AB is 4 cm and the length of the arc AB is 5 cm. Find the central angle \[Theta], in radians, correct to 6 decimal places.

Thanks

2. Originally Posted by swimmerxc
I need help with these two, I don't get it.

1. Use Newton's method to find a zero of the function, f(x)=x^3-3 x+6, using x[0]=-1. Explain why the method fails. Fix it so that it does find a zero.
f'(-1) = 0. this will result in a division by zero using Newton's method, so it will fail for the initial guess of x_0 = -1. to fix this, simply guess a new approximation. x_0 = -2 is a better one

3. thanks i get the first one, but i forgot all my trig and have no idea how to do the second one