Assume that Q, R, and S are the angles of a triangle, with opposite sides q, r, and s respectively. Select all of the following that represent the law of cosines. q2 = r2 + s2 – 2rscos(Q) . q2 = r2 + s2 – 2qscos(R) . r2 = q2 + s2 – 2qscos(Q) . r2 = q2 + s2 – 2qscos(R) .s2 = q2 + r2 – 2qrcos(S)