Question

in a pitched roof the acute angle formed by the intersection of two slopes is called

Answer 1

"Suppose they are m1 and m2.  Since the

slope of a line is the tangent of its angle of elevation, the angle

between the lines is the difference in the two angles.  Thus, if theta

is the angle between, and A and B are the angles of elevation of the

two lines,

                                         tan(A) - tan(B)            m1 - m2

tan(theta) = tan(A - B) = -------------------      =  -----------

                                           1 + tan(A)tan(B)        1 + m1*m2

"