SAS congruence of triangles: If any two sides and included angle (angle between those sides) of one triangle are equal to corresponding two sides and included angle of second triangle, then the two triangles are condruent by SAS rule
Angle BAC is the included angle of sides AB and AC in triangle ABC
Angle DCA is the included angle of sides CD and AC in triangle CDA
If the null hypothesis, is rejected, then we can conclude that the correlation coefficient is significant. This means that there is enough evidence to conclude that a relationship exists between the two (or more) variables involved in the regression.