Simplify (x^2+4)(2x^2+x-1)

2x^4+x^3-x^2+8x^2+4x-4=2x^4+x^3+7x^2+4x-4

EXPAND THE BRACKETS. 
1st value in the 1st bracket multiplied with the 1st value in the 2nd bracket plus the 1st value in the first bracket multiplied with the 2nd value in the 2nd bracket etc.
So...
(x^2 X 2x^2) + (x^2 X x) + (x^2 X -1) + (4 X 2x^2) + (4 X x) + (4 X -1)
 = 2x^4 + x^3 - x^2 + 8x^2 + 4x - 4
 = 2x^4 + x^3 + 7x^2 + 4x - 4