a)=3x^2+21x-(3x^2+2x-9x-6)=3x^2+21x-3x^2-2x+9x+6=28x+6
b) =4x^2+4x+1+4(x^2-6x+9)
=4x^2+4x+1+4x^2-24x+36
=8x^2-20x+37.

a) 3x(x + 7) - (x - 3)(3x + 2)
= 3x^2 + 21x - (3x^2 - 7x - 6)
= 3x^2 + 21x - 3x^2 + 7x + 6
= 28x + 6
b) (2x+ 1)^2 + 4(x - 3)^2
= 4x^2 + 4x + 1 + 4x^2 - 24x + 36
= 8x^2 - 20x + 37
 

bạn ơi 2 câu sau bạn ib riêng tui giải cho nhé
a) 3x(x + 7) - (x - 3)(3x + 2)
= 3x^2 + 21 - 3x^2 - 2x + 9x + 6
= 7x + 27
b) (2x + 1)^2 + 4(x - 3)^2
= 4x^2 + 4x + 1 + 4x^2 - 24x + 36
= 8x^2 - 20x + 37

a) 3x(x + 7) - (x - 3)(3x + 2)
= 3.x^2 + 21x - 3.x^2 + 7x + 6
= 28x + 6

b) (2x + 1)^2 + 4.(x - 3)^2
= 4.x^2 + 4x + 1 + 4(x^2 - 6x + 9)
= 4.x^2 + 4x + 1 + 4.x^2 - 24x + 36
= 8.x^2 - 20x + 35

c) (2x + 5)^2 - 4x(x - 3)
= 4.x^2 + 20x + 25 - 4.x^2 + 12x
= 32x + 25

d) (2x - 3)^3 - (2x + 3)^3
= 8.x^3 - 36.x^2 + 54x - 27 - 8.x^3 - 36.x^2 - 54x - 27
= -72.x^2 - 54

a)3x(x+7)-(x-3)(3x+2)
=3x^2+21x-3x^2+9x-2x+6
=27x+6
b)(2x+1)^2+4(x-3)^2
=4x^2+4x+1+4x^2-24x+36
=8x^2-20x+37
c)(2x+5)^2-4x(x-3)
=4x^2+20x+25-4x^2+12x
=32x+25
d)(2x-3)^3-(2x+3)^3
=8x^3-36x^2+54x-27-8x^3-36x^2-54x-27
=-72x^2-54