數學-一元二次方程式題目

前兩題題目沒打清楚
不過題目大概是求......bx的二次方-30x+9，求b？
30=2*(根號b) *3
=>(根號b)=5
=>b=259x的二次方+cx+16，求c？
c=+-2*3*4
=+-24解下列一元二次方程式：
1. (x+3)的二次方=19
=>x+3=+-(根號19)
=>x=-3+-(根號19) 2. 9(x-2)的二次方-16=0
=>9(x-2)^2=16
=>3(x-2)=+-4
=>3x-6=+-4
=>x=(6+-4)/3
=>x=10/3 or 2/3 3. 2x的二次方-8x-1792=0
=>x^2-4x-896=0
=>x^2-4x+4=900
=>(x-2)^2=30^2
=>x-2=+-30
=>x=2+-30
=>x=32 or -28 4. 3x的二次方+5x+1=0
=>x=[-3+-根號(25-12)]/6
=>x=[-3+-(根號13)]/6 5. 9x的二次方+4=12x
=>9x^2-12x+4=0
=>(3x-2)^2=0
=>3x-2=0
=>x=2/3(重根) 6. -3x的二次方-6x+6=2x的二次方-x+2
=>5x^2+5x-4=0
=>x=[-5+-根號(25+80)]/10
=>x=[-5+-(根號105)]/10恩
大概就這樣
如果有誤請通知
Thanks~

sol
(b)x^2-30x+9
=(sqrt (b)*x)^2-2(3)(5x)+3^2
=(sqrt(b)*x-3)
b=25

9x^2+cx+16
=(3x)^2+2(3x)(4)+4^2
c=2*3*4
=24
(x+3)^2=0
x=-3

sor I haven't learn more about this...sor(form 3 only...)