7 4x 2 5x 8 July 8, 2019 16 32 64 128 7 4x 2 5x 8 if x =- 2 7 5x 2 8x =- 4x 3 x 2x 7 4x 8x 2 5x 4x 2 5x 7 )+( 3x 2 8x 12 5x 7 )( 9x 2 4x 8 8x 2 4x 2 5x 7 4x y 7 5x 8y 2 7 2 5x )+ 27 18x 3 8 4x 10 8x 2 7 =- 4x 5x 4x y 7 5x 8y 2 substitution 5x 8 3 4x 7 2