<span>1st number = 9, 2nd number = 6, 3rd number = -4 </span>
If you mean to find 4 cos(2<em>a</em>), then recall the double angle identity for cosine:
cos(2<em>x</em>) = 2 cos²(<em>x</em>) - 1
so that
4 cos(2<em>a</em>) = 4 (2 cos²(<em>x</em>) - 1) = 4 (√3 - 1)
M=-5, b=-2 hope this helps