10x^2+20+71=9
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1 Answer

Simplify: 10x2+20x=9-71=-62

To solve by completing the square:

Divide through by 10: x2+2x=-6.2

Complete the LHS square: x2+2x+1=-6.2+1 (1 has to be added to RHS as well to preserve equality)

We have a perfect square on the left:

(x+1)2=-5.2 which cannot be solved for real numbers because no perfect square can be negative. This suggest an error in the question. For a solution the RHS must be positive.

If the quadratic had been 10x2+20x-71=9, then:

10x2+20x=80

x2+2x=8 after dividing through by 10

Complete the square:

x2+2x+1=8+1=9

(x+1)2=9

x+1=3 or -3 making x=2 or -4.

[The equation becomes 10(x2+2x-8)=0, which factorises 10(x-2)(x+4)=0]

by Top Rated User (1.2m points)

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