紅色格格果D唔色做

In fact, the expression in red rectangle is obtained by applying S k dx=k*S dx=kx+c and S x^n dx= 1/(n+1) * x^(n+1) +c , where c is constant
If you read the rule above before while you are reading the chapter, you may be able to fic the problem :)

1. dy/dx =S (6x-4) dx
y=S 6x dx -S 4 dx
Then applying the rule,
y=3x^2- 4x + c
where c is a constant.

2.dy/dx=3x^2-4x+1
y=S (3x^2-4x+1) dx
y=S 3x^2 dx - S4x dx +S dx
y=x^3 - 2x^2 + x +c
where c is a constant

Hope I can help you!