Question

Solve -3x2 + 30x - 90 = 0.
solve with completing the square or quadratic formula.
the answer should be a complex number
i will reward a medal

Answer 1

multiply with -1
3x2-30x+90=0
divide by 3
x2-10x+30=0
x2-2*5*x+25+5=0
(x-5)^2=-5
x-5=(-5)^1/2
x=5+i*5^1/2

Answer 2

@marinesrock

Answer 3

lets use quadratic formula:

\[\frac{ -30 \pm \sqrt{30^{2}-4(-3)(-90)} }{ 2(-3) }\]

reduces to:

\[\frac{ -30 \pm \sqrt{-180} }{ -6 }\]

take the negative out of square root with i and you get:

x = 2.76i and 7.24i

Answer 4

ok thanks