Which of the following is not a quadratic equation? 

For equation: $x(5x-28)+87=3x^2+2x^2-55$ 

$\Rightarrow 5x^2-28x+87=5x^2-55$

$\Rightarrow 28x-142=0$, which is not a quadratic equation. 

For equation: $x^2(x+5)=(x+1)(x+2)(x+3)$ 

$\Rightarrow x^3+5x^2=x^3+6x^2+11x+6$ 

$\Rightarrow x^2+11x+6=0$, which is a quadratic equation. 

For equation: $x^2+5x=5x+9$ 

$\Rightarrow x^2-9=0$, which is a quadratic equation. 

For equation: $(x-1)(x+1)=5$ 

$\Rightarrow x^2-1=5$ 

$\Rightarrow x^2-6=0$, which is a quadratic equation. 

Hence, among the given equations $x(5x-28)+87=3x^2+2x^2-55$ is not a quadratic equation.