Let P be the plane in R3 given by the general equation x + 2y − 2z = 4 and let Q be the plane in R3 given by the general equation 2x − y − 2z = 3. Which of the following is the angle of intersection of the planes P and Q?

Let P be the plane in R
3 given by the general equation x + 2y − 2z = 4 and let Q be the plane
in R
3 given by the general equation 2x − y − 2z = 3. Which of the following is the angle of
intersection of the planes P and Q?