C1: 3x2. (2x3-x+5)
= 6x5 - 3x3+ 15x2
hệ số : 6
C2:
5x(12x+7) - 3(20x-5) = -100
⇔60x2+35x- 60x+15=-100
⇔ 60x2-25x+115=0
⇔ 12x2-5x+23=0
⇔ \(\left[{}\begin{matrix}\frac{5+\sqrt{25-1104}}{24}\\\frac{5-\sqrt{25-1104}}{24}\end{matrix}\right.\)
⇔ \(\left[{}\begin{matrix}\frac{5+\sqrt{-1079}}{24}\\\frac{5-\sqrt{-1079}}{24}\end{matrix}\right.\)
x ∉ R
C3: 3x.(x-2) - 5x. (1-x) - (8x2-3)
= 3x2 - 6x - 5x + 5x2 - 8x2 +3
= -11x+3