Thu gọn biểu thức
1,\(\left(x-3\right)\cdot\left(x+3\right)-\left(x+1\right)^2\)
2, \(\left(2x-1\right)^2-\left(x+2\right)^2-\left(2x-\dfrac{1}{2}\right)^2\)
3,\(\left(2x+1\right)^3-\left(2x-1\right)^3-24x^2\)
4, \(\left(x-2\right)^3-\left(2x+3\right)^3-7\cdot\left(1-x\right)^3\)