<P> A dihedral angle is the angle between two intersecting planes . In chemistry it is the angle between planes through two sets of three atoms, having two atoms in common . In solid geometry it is defined as the union of a line and two half - planes that have this line as a common edge . In higher dimension, a dihedral angle represents the angle between two hyperplanes . </P> <P> When the two intersecting planes are described in terms of Cartesian coordinates by the two equations </P> <Dl> <Dd> a 1 x + b 1 y + c 1 z + d 1 = 0 (\ displaystyle a_ (1) x + b_ (1) y + c_ (1) z + d_ (1) = 0) </Dd> <Dd> a 2 x + b 2 y + c 2 z + d 2 = 0 (\ displaystyle a_ (2) x + b_ (2) y + c_ (2) z + d_ (2) = 0) </Dd> </Dl> <Dd> a 1 x + b 1 y + c 1 z + d 1 = 0 (\ displaystyle a_ (1) x + b_ (1) y + c_ (1) z + d_ (1) = 0) </Dd>

In a polypeptide chain the bond angles φ and ψ are