trigonometry, grade 10, question 11

27/01/2017 Grade 10 135
  1. Verify that (2x2-1)(x+2)=2x3+4x2-x-2.
  2. Given:E= 2{\cos^3}a-4{\sin^2}a-cosa+2

    , find cos a if E=0 knowing that 90<a<180