How do you solve the trigonometric equation sin(x)+x=9?

Rihanna Bentley

Rihanna Bentley

Answered question

2022-11-14

How do you solve the trigonometric equation sin ( x ) + x = 9?
How do you solve the trigonometric equation sin ( x ) + x = 9? More generally, how do you solve equations with both trigs and 'x's without graphing? And maybe I only want real number answers.
Suggestions and edit: If you use the Taylor Series, you will basically end up with at least 6 t h degree equations, if you want to make it close. Equation Solvers Are NOT Allowed. That will kind of limit you to this:(assuming you make careless mistakes, just like me, so you don't want cubic equations)
x + x = 9.
This yields x = 4.5, which is DEFINITELY a bad estimation.
Thanks for helping me! It's just that I don't know what Newton-Ralphson and iterations are. Can you explain it to me or give me a link?

Answer & Explanation

h2a2l1i2morz

h2a2l1i2morz

Beginner2022-11-15Added 19 answers

The function sin x + x 9 has the strictly non-negative derivative cos x + 1, so the solution in R is unique, confined to [ 8 , 10 ]. The Newton-Raphson method x x sin x + x 9 cos x + 1 iteratively improves the estimate x 0 = 8 to 8.0125448260685 (according to my Python), if that's accurate enough.

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