In an elastic collision between two bodies of mass m1 and m2, with m2 initially at rest, mass 1 moves off at angle q relative to the direction of its initial velocity and mass 2 at angle f. an exam paper shows the equations below:
m1v1i= m1v1fcosq + m2v2fsinf
0 = m1v1fsinq + m2v2fcosf
what error(s) has the student made?

a. in the first equation, m_2v_2f sin/should be m_2v_2fcosf.
b. in the second equation, m_2v_2fcos f should bem_2v_2fsinf.
c. in the second equation, the plus sign between the terms on the right should be a minus sign
d.. all of the errors listed above.
e. only errors (a) and (b) above.