Ruby and math module to solve trig functions

Question

So I'm trying to practice using Ruby to solve trig functions and I'm having some difficulty getting the Math library to work.

The trig function is: y = (x^3 sqrt(2x^2)) / (sin(x+5)) where x = 51, and the answer needs to be in degrees. The problem is supposed to be solved in Matlab, which I have no experience with, but I managed to hack together the following output for the function: 1.1540e + 07, and I want to verify that what I'm doing in Matlab is correct, so I want to use Ruby to make sure the answer is what I'm supposed to be getting.

The Ruby code I'm trying to use to solve this function is: puts ((51 ** 3)Math.sqrt(2(51 ** 2)) / (Math::sin(56.degrees))) however when running the code I get the following errors:

/Users/sam/Desktop/jasons_shit.rb:1: syntax error, unexpected tCONSTANT, expecting ')'
puts ((51 ** 3)Math.sqrt(2(51 ** 2)) / (Math::sin(56.degrees)))
                   ^
/Users/sam/Desktop/jasons_shit.rb:1: syntax error, unexpected '(', expecting ')'
puts ((51 ** 3)Math.sqrt(2(51 ** 2)) / (Math::sin(56.degrees)))
                           ^
/Users/sam/Desktop/jasons_shit.rb:1: syntax error, unexpected ')', expecting end-of-input
puts ((51 ** 3)Math.sqrt(2(51 ** 2)) / (Math::sin(56.degrees)))

How can I go about evaluating this function and resolving the errors?

@NKN Ruby. I want to double check the answer I got out of Matlab using Ruby's Math functions. — Sam Lim, Apr 10 '17 at 00:35
@NKN and I don't know what's up with the errors I'm getting using Ruby's Math library — Sam Lim, Apr 10 '17 at 00:35
Is it possible that you need to add `*` where you want to multiply? As in: `puts ((51 ** 3)*Math.sqrt(2*(51 ** 2)) / (Math::sin(56.degrees)))` — Craig, Apr 10 '17 at 02:58

score 2 · Accepted Answer · answered Apr 10 '17 at 00:36

You need to have * each time you multiply, and try changing degrees to radians:

x = 51
p (x ** 3) * Math.sqrt(2 * x ** 2) / (Math::sin((x+5) * Math::PI / 180))

You also don't need so many paranthesis because Ruby understands mathematical order of operations.

NKN · Answer 2 · 2017-04-10T00:47:29.417

As the error is telling you, some ( and * are missing.

Since the intended variable should be in Radians, so you should convert first to from degrees to radians and then do the calculation.

xindeg = 51
xinrad = xindeg*Math::PI/180
puts xinrad ** 3 * Math.sqrt(2*xinrad ** 2) / Math::sin(xinrad+5*Math::PI/180)

1.070855715686936

Also in MATLAB, the correct way is as follows:

x=51
xinrad = x*pi/180;
y = (xinrad^3 * sqrt(2*xinrad^2)) / (sin(xinrad+5*pi/180))

y =

1.070855715686936

Ruby and math module to solve trig functions

2 Answers2