What is the sine, cosine, and tangent of the real number − π/4

And how did you solve that answer?

Thanks!

The line y=x makes an angle of TT/4 with the positive x-axis. So we get from the equation of the unit circle
x^2+y^2=1
x^2+x^2=1, (since we are using the line y=x)
2x^2=1
x^2=1/2
y=x=sqrt(1/2)=sqrt(2)/2
Since sin(t)=y and cos(t)=x it follows that
sin(TT/4)=sqrt(2)/2 and cos(TT/4)=sqrt(2)/2

That angle corresponds to -45º.

Draw a unit circle, draw the radius that makes an angle of 45º BELOW the x axis, draw the segments for the sine and cosine, apply Pythagoras' Theorem to the right triangle thus formed and go study how the tangent is related to the sine and cosine.

In general, you haven't studied (or understood) Trig, so this is a good time to give a crack.