Solve -x^2+81=0 using two methods

Solve using at least two different methods
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1 Answer

(1) -x2+81=0, so 81=x2, which is the same as x2=81.

Taking square roots of each side: x=±9, so x=9 or -9.

(2) -x2+81=81-x2=(9-x)(9+x)=0 after factorising.

So either 9-x=0, making x=9; or 9+x=0, making x=-9.

by Top Rated User (1.2m points)

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