How do we solve this?

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1 Answer
David G.
Aug 31, 2017

#x=sqrt20 i ~= 4.47i#

Explanation:

#-4x^2-80=0#

Add 80 to both sides:

#-4x^2=80#

Multiply both sides by #-1#:

#4x^2 = -80#

Divide both sides by #4#:

#x^2 = cancel(-80)/cancel(4)=-20#

Now, with 'normal' numbers we cannot take the square root of a negative number, but with 'imaginary' numbers we can. The square root of #-1# is written as #i#:

#x^2 = 20xx-1#

#x=sqrt(20)xxsqrt(-1)#

#x=sqrt20 i ~= 4.47i#

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