If it's not what You are looking for type in the equation solver your own equation and let us solve it.
-21x^2+81=0
a = -21; b = 0; c = +81;
Δ = b2-4ac
Δ = 02-4·(-21)·81
Δ = 6804
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$
The end solution:
$\sqrt{\Delta}=\sqrt{6804}=\sqrt{324*21}=\sqrt{324}*\sqrt{21}=18\sqrt{21}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18\sqrt{21}}{2*-21}=\frac{0-18\sqrt{21}}{-42} =-\frac{18\sqrt{21}}{-42} =-\frac{3\sqrt{21}}{-7} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18\sqrt{21}}{2*-21}=\frac{0+18\sqrt{21}}{-42} =\frac{18\sqrt{21}}{-42} =\frac{3\sqrt{21}}{-7} $
| -1+4k=1+5k | | X+(x(4)=192 | | M-5=-m-9 | | 12x-3-3x=12 | | x+x+x*0.5+x*0.25+3=300 | | 10x+80=300 | | -3(x=10)=-60 | | X+(x-4)=193 | | K+81+5k=75 | | -0.5x=-22 | | 0=2x(2.718^(2x))+(2.718^(2x)) | | 31=x/4+14 | | 3(x+4)+3x=12+3(3x+3) | | 27=11x+16 | | 30=2.5x+x | | 6(x+1)+5=3x(2+x) | | 9u-2=61 | | 2x+6(5x−5)=130 | | 12=3=3u | | -7z-49=-7 | | 4z/9+6=-1 | | -2(x=1/3)+9=4 | | 2r-15=3r+2 | | -5m=-22.5 | | 68.88x+45=1.99 | | -3+m=7.5 | | -2x-2=2x-4 | | 720=-3r-10(-7r-5) | | n02+1=−2 | | -4+3w=-28 | | -4+m=-8.5 | | 2.25/x/33=x |