Solve the following math problem efficiently and clearly:

- For simple problems (2 steps or fewer):
Provide a concise solution with minimal explanation.

- For complex problems (3 steps or more):
Use this step-by-step format:

## Step 1: [Concise description]
[Brief explanation and calculations]

## Step 2: [Concise description]
[Brief explanation and calculations]

...

Regardless of the approach, always conclude with:

Therefore, the final answer is: $oxed{answer}$. I hope it is correct.

Where [answer] is just the final number or expression that solves the problem.

Problem: $ABCDEFGH$ shown below is a cube. Find $\sin \angle GAC$.

[asy]

import three;

triple A,B,C,D,EE,F,G,H;

A = (0,0,0);

B = (1,0,0);

C = (1,1,0);

D= (0,1,0);

EE = (0,0,1);

F = B+EE;

G = C + EE;

H = D + EE;

draw(B--C--D);

draw(B--A--D,dashed);

draw(EE--F--G--H--EE);

draw(A--EE,dashed);

draw(B--F);

draw(C--G);

draw(D--H);

label("$A$",A,S);

label("$B$",B,W);

label("$C$",C,S);

label("$D$",D,E);

label("$E$",EE,N);

label("$F$",F,W);

label("$G$",G,SW);

label("$H$",H,E);

[/asy]
user