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

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

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

• Are you using a calculator or not? – Bobson Dugnutt Apr 23 '17 at 20:09
• Yes using a calculator – Alex Vincent Apr 23 '17 at 20:09
• Are you in radians? – John Doe Apr 23 '17 at 20:10
• I haven't checked, but I would guess you might have set your calculator to calculate in degrees, instead of radians. – Bobson Dugnutt Apr 23 '17 at 20:10
• Yes i am...jdfk – 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. $\sin^2(x)=(\sin(x))^2\neq\sin(x^2)$
• First, calculate $\sin(\frac{2\pi}{7})$. Then, square that whole thing. You're squaring the angle first. – user12345 Apr 23 '17 at 20:13