I'm trying to calculate

$$\sin^2(2\pi/7) \cdot (2/1.05)$$

But not getting the right answer ($1.164$)

Can someone break it down step by step. I'm doing

$\sin(2\pi/7)^2\cdot(2/1.05) = 1.37$??

  • $\begingroup$ Are you using a calculator or not? $\endgroup$ – Bobson Dugnutt Apr 23 '17 at 20:09
  • $\begingroup$ Yes using a calculator $\endgroup$ – Alex Vincent Apr 23 '17 at 20:09
  • $\begingroup$ Are you in radians? $\endgroup$ – John Doe Apr 23 '17 at 20:10
  • $\begingroup$ I haven't checked, but I would guess you might have set your calculator to calculate in degrees, instead of radians. $\endgroup$ – Bobson Dugnutt Apr 23 '17 at 20:10
  • $\begingroup$ Yes i am...jdfk $\endgroup$ – Alex Vincent Apr 23 '17 at 20:10

You are calculating $$\sin\Bigl(\left(\frac{2\pi}{7}\right)^2\Bigr)\cdot\frac{2}{1.05}\approx1.37$$ This is NOT the same as $$\sin^2\Bigl(\frac{2\pi}{7}\Bigr)\cdot\frac{2}{1.05}\approx1.164$$ I.e. $\sin^2(x)=(\sin(x))^2\neq\sin(x^2)$

  • $\begingroup$ How do you calculate the second one then? $\endgroup$ – Alex Vincent Apr 23 '17 at 20:12
  • 2
    $\begingroup$ First, calculate $\sin(\frac{2\pi}{7})$. Then, square that whole thing. You're squaring the angle first. $\endgroup$ – user12345 Apr 23 '17 at 20:13
  • $\begingroup$ Ah, thank you very much. I'll mark you right answer $\endgroup$ – Alex Vincent Apr 23 '17 at 20:15
  • $\begingroup$ Glad I could help. If there's any more confusion, the last line of the post should clear it pretty well. $\endgroup$ – user12345 Apr 23 '17 at 20:21

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