Question

How do you solve `(r-2)(r+6)=4` using the quadratic formula?

Answer 1

Solution: `r=2.47(2dp) or r= -6.47(2dp)`

Explanation:

`(r-2)(r+6)=4 or r^2+4r-12=4 or r^2+4r-16=0 or (r+2)^2-4-16=0 or (r+2)^2=20 or r+2 = +-sqrt(20) or r+2=+-2sqrt5 :. r= -2+2sqrt5=2(-1+sqrt5)=2.47(2dp) =or r= -2-2sqrt5= 2(-1-sqrt5)=-6.47(2dp)`
Solution: `r=2.47(2dp) or r= -6.47(2dp)`

Using Quadratic formula:`(r=-b/(2a)+-sqrt(b^2-4ac)/(2a))`

`r^2+4r-16=0 ; a=1 ;b= 4 ;c=-16 ; b^2-4ac=80 ; r= -4/2+- sqrt80/2= -2+-2sqrt5:. r_1=2.47(2dp) or r_2=-6.47(2dp)`
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