Question 321269
A^2+B^2=C^2
X^2+X^2=6^2
2X^2=36
X^2=36/2
X^2=36/2
X^2=18
X=SQRT18
X=SQRT9*2=3SQRT(2) ANS. D)
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X^2+X^2=(X+9)^2
2X^2=X^2+18X+81
2X^2-X^2-18X-81=0
X^2-18X-81X=0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
x=(18+-sqrt-18^2-4*1*-81])/2*1
x=(18+-sqrt[324+324])/2
x=(18+-sqrt648)/2
x=(18+-25.456/2
X=(18+25.456)/2
X=43.456/2
X=21.728 ANS.
PROOF:
2*21.728^2=(21.728+9)^2
2*472.11=30.728^2
944.21=944.21