要有步驟..THX...有數學問題..好急用..有心人help我答

1.(3a^2)^2
= 3^(1*2) a^(2*2)
= 3^2 a^4
= 3*3 a^4
= 9a^4
---------
求多項式3x^2-2x+1在下列各情況中的值
1.x=2
= 3(2)^2 - 2(2) + 1
= 3*2^2 - 2*2 + 1
= 3*4 - 4 + 1
= 81 - 4 + 1
= 78
---------
化簡下列各式,並按變數的降冪排列表示答案.
1.(5a+a^2+3)-(7-a+a^2)
= 5a + a^2 + 3 - 7 - (-a) - (a^2)
= 5a + a^2 + 3 - 7 + a - a^2
= a^2 - a^2 + 5a + a + 3 - 7
= 5a + a + 3 - 7
= 4a + 3 - 7
= 4a - 4
= 4(a-1)
----------
展開下列各式.
1.-5x(x^2-2x+3)
= -5x(x^2) - (-5x)(2x) + (-5x)(3)
= -5x^(1+2) - (-5*2 x^2) + (-5*3 x)
= -5x^3 - (-25x^2) + (-15x)
= -5x^3 + 25x^2 - 15x
= -5(x^3 - 5x^2 + 3x)
= -5x(x^2 - 5x + 3)

2.(3x-4y)^2
= (3x-4y)(3x-4y)
= (3x)(3x) - (4y)(3x) - (3x)(4y) - (4y)(4y)
= (3*3 x*x) - (4*3 xy) - (3*4 xy) - (4*4 y*y)
= 9x^2 - 12xy - 12xy - 16y^2
= 9x^2 - 24xy - 16y^2

展開下列各式,並按變數的降冪排列表示答案.

1.(n+6)(2n^2+9n-1)
= (n)(2n^2) + (n)(9n) + (n)(-1) + 6(2n^2) + 6(9n) + 6(-1)
= 2n^(1+2) + 9n^(1+1) + (-n) + (6*2 n^2) + (6*9 n) + (-6)
= 2n^3 + 9n^2 - n + 12n^2 + 54n - 6
= 2n^3 + 9n^2 + 12n^2 - n + 54n - 6
= 2n^3 + (9+12)n^2 + (54-1)n - 6
= 2n^3 + 21n^2 + 53n - 6

2.(3b-2b^2+4)(5-b)
= (3b)(5) + (-2b)(5) + (4)(5) + (3b)(-b) + (-2b)(-b) + (4)(-b)
= (3*5 b) + (-2*5 b) + (4*5) + (-3 b^(1+1) ) + (2 b^(1+1) ) + (-4b)
= (15b) + (-10b) + (20) + (-3b^2) + (2b^2) + (-4b)
= 15b - 10b + 20 - 3b^2 + 2b^2 - 4b
= -3b^2 + 2b^2 + 15b - 10b - 4b + 20
= (-3+2)b^2 + (15-10-4)b + 20
= -b^2 + b + 20

其實我想問下究竟.(3b-2b^2+4)(5-b)裡面既^等於什麼????????