Does 7x²+9+3x = 10x²+9? Subtract 9 from each side: 7x²+3x=10x², subtract 7x² from each side: 3x=3x², so x=x² and x²-x=0. Therefore x(x-1)=0 and x=0 or 1. So the original equation is only true when x=0 or 1, and is not true for other values of x. Therefore the two expressions are not equivalent, and the second is not a simplification of the first. But 7x²+9+3x² can be simplified to 10x²+9.