Can someone help me with this math question?

In triangle abc, the length of side ab is 12 cm, the length of side bc is 5 cm, and the length of side ca is 9 cm. find the measure of angle a using the law of cosines.

Which shows the correct substitution of the values a,b and c from the equation 1=-2x+3x^2+1

Thomas is using a drawing program to complete a construction. which construction could he be completing? two perpendicular lines are drawn. inscribing an equilateral triangle in a circle inscribing a square in a circle inscribing a regular pentagon in a circle inscribing a regular hexagon in a circle