Question

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( x - 9 )² = x² - 40  

Answer 1

$(x-9)^{2} = x^{2} -40 \\ \\ \\ (x-9)*(x-9)= x^{2} -40 \\ \\ x^{2} -9x-9x+81= x^{2} -40 \\ \\ x^{2} -18x+81- x^{2} +40=0 \\ \\ -18x+121=0 \\ \\ -18x=-121 \\ \\ x= \frac{-121}{-18} \\ \\ x=6,72...$