How do you calculate arcsin (-1/ sqrt 2)arcsin(12)?

1 Answer
Jul 20, 2015

Use properties of right angled triangle with sides 1/sqrt(2)12, 1/sqrt(2)12 and 11 to find arcsin(-1/sqrt(2)) = -pi/4arcsin(12)=π4

Explanation:

arcsin(-1/sqrt(2)) = alphaarcsin(12)=α where alpha in [-pi/2, pi/2]α[π2,π2] such that sin(alpha) = -1/sqrt(2)sin(α)=12

1/sqrt(2)12 is one side of the right angled triangle with sides:

1/sqrt(2)12, 1/sqrt(2)12 and 11

(Note (1/sqrt(2))^2 + (1/sqrt(2))^2 = 1/2 + 1/2 = 1 = 1^2(12)2+(12)2=12+12=1=12)

This triangle has angles pi/4π4, pi/4π4 and pi/2π2.

So sin(pi/4) = 1/sqrt(2)sin(π4)=12

Now sin(-theta) = -sin(theta)sin(θ)=sin(θ)

So sin(-pi/4) = -1/sqrt(2)sin(π4)=12

So arcsin(-1/sqrt(2)) = -pi/4arcsin(12)=π4