If it's not what You are looking for type in the equation solver your own equation and let us solve it.
k^2+21=0
a = 1; b = 0; c = +21;
Δ = b2-4ac
Δ = 02-4·1·21
Δ = -84
Delta is less than zero, so there is no solution for the equation
| f^2-33=-29 | | 27=5v+8/3+7v-1/5 | | d^2-64=0 | | 5z-1.75=8.26 | | -6f+3.1=60-7 | | -6f+3.1=60 | | (11x-50)=90 | | 5+3x=6+x+2 | | 10x-48)=68 | | 1.25+2.5-0.5x+1.75=0 | | X+20=6r | | 22x-4=7 | | 5x+3(20-x)=74 | | -3+m=-1 | | 1/2n=-5 | | -8=e(4) | | 196+k=151 | | 2r+1.6=13.6 | | 937+w=887 | | 3(-2+4y)-14y=-4 | | 3(-2+4y)-14=-4 | | -5x=212.5 | | 5x+14+3x+2=30 | | 2b+33(b+12)-6=70 | | 3x+1+3x-1=90 | | Y=-3x^2+21x+6 | | 85=(4x+21) | | 74-x=18 | | 68-4x=46 | | 2x-(26+5x)=-8 | | 3+3x-8=13 | | 0=3x^2-84 |