`-3x^3*(4x^5+7x^2)`
`= -3x^3 * 4x^5 - 3x^3 * 7x^2`
`= -12x^8 - 21x^5`
`->` D
..............................................
`(3x+5)(2x-1)+(5-6x)(x+2)=x`
`⇔ 6x^2 + 7x - 5 - 6x^2 - 7x + 10 = x`
`⇔ (6x^2-6x^2) + (7x-7x) + (10-5) = x`
`⇔ x = 5`
`->` C
.................................................
`(1/2x-0,5)^2`
`= (1/2x)^2 - 2*1/2x*0,5+0,5^2`
`= 1/4x^2 - 0,5x + 0,25`
`->` C
