Solve Equation w/ Arcsin: How to Get 1/sqrt2 from pi/4

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Hello, I was trying to solve an equation with arcsin and I wasn´t sure about the result so I tried wolfram alpha with step by step solution and there is one step that I don´t understand, the one where you take the sine of both sides. How can I get 1/sqrt2 from pi/4 ? Thanks for help.View attachment 4961

 

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sin(pi/4) = 1/sqrt(2) is probably the most well-known trigonometric value (it comes from the isosceles right angle triangle).