Q) how to solve by completing the square method ? a) 2x^2+16x+5 b) 6+4x-x^2

1 Answer
Dec 25, 2017

a)Solution: x~~ -0.33 , x~~-7.67
b)Solution: x~~ -1.16 , x~~ 5.16

Explanation:

a) 2x^2+16x+5=0 or 2(x^2+8x) +5=0 or

2(x^2+8x+16)-32 +5=0 or

2(x+4)^2=27 or (x+4)^2=27/2 or (x+4)^2=13.5 or

(x+4)=+-sqrt13.5 or x ~~-4+-3.674 or

x ~~-4+-3.674 :. x~~ -0.33(2dp) , x~~-7.67(2dp)

Solution: x~~ -0.33 , x~~-7.67 [Ans]

b) -x^2+4x+6=0 or -(x^2-4x) +6=0 or

-(x^2-4x+4) +4+6=0 or (x^2-4x+4)=10 or

(x-2)^2=10 or x-2 = +-sqrt10 or

x = 2+-sqrt10:. x ~~ 5.16(2dp) , x~~ -1.16(2dp)

Solution: x~~ -1.16 , x~~ 5.16 [Ans]