The slopes of the regression lines are given by the coefficients of x in the equations. So, the slopes are −1∕2 and −2∕3. Let θ be the acute angle between the lines. Then, we have: tanθ=|
−1
2
−
−2
3
1+
−1
2
⋅
−2
3
|=
1
8
. Using the triple angle formula for tangent, we get: tan3θ=