Math.acos gives me a different value than my calculator

Question

In Ruby,

Math.acos(10/70) * 57.2958

should return approximately 80 degrees (according to my calculator). However it is returning approximately 90 degrees. Why is that?

Use `10.quo(70)` instead of `10/70`. – Stefan May 22 '16 at 13:32 — Stefan, May 22 '16 at 13:32

score 2 · Accepted Answer · answered May 22 '16 at 13:05

2

You need to add decimal points, or Ruby will assume integer division:

irb(main):006:0> Math.acos(10/70) / Math::PI * 180
=> 90.0
irb(main):007:0> Math.acos(10.0/70) / Math::PI * 180
=> 81.78678929826181

If you just use 10/70, this will round to 0, and you get Math.acos(0) instead of Math.acos(0.14..) which is what you want.

answered May 22 '16 at 13:05

Arc676

1 Answers1