✔ 最佳答案
2x^2-7x+12=0
Before beginning the "complete the square" process, the coefficient of the x^2 term MUST be +1
x^2-(7/2)x+6=0
x^2-(7/2)x= -6
x^2-(7/2)x+ ?= -6+?
? is always half the coefficient of the x term, squared. Add to both sides!
x^2-(7/2)x+49/16= -6+49/16
(x-7/4)^2= -96/16+49/16
(x-7/4)^2= -47/16
Now take the square root of both sides
x-7/4=+/-rt(-47) / 4
The rt(-47) poses a problem, because you cannot
take the square root of a negative number. We get
around that as follows
x-7/4=[rt(47)rt(-1)] / 4
Now rt(-1) = i
x-7/4= +/-rt(47)i / 4
x=7/4+/-rt(47)i/4
This is a Complex Number, and Complex Numbers
are written in the form a+bi, where a and b are Real
Numbers, and i =sq.rt.(-1)
Therefore we write our answer as
x=7/4+rt47)i/4, or
x=7/4-rt(47)i/4
Note. I knew I was headed for Complex roots, because the Discriminant of 2x^2-7x+12 is
b^2-4ac, where a=2, b=-7, c=12
b^2-4ac=(-7)^2-4(2)12
=49-96
=-47
It's negative, therefore Complex Solution only