how do you solve 2??(?? + 4) - (?? - 8)

Question

What is wrong with this equation?

2??(?? + 4) − (?? − 8)
2??
2 + 8?? − ?? − 8
2??
2 + 7?? − 8

Answer 1

Hi Felicia,

 

I am going to assume that ?? is just another variable that I can replace with x.

 

The equation then becomes 2x(x+4) - (x-8) which reduces to 2x^2+8x-x+8 which can further be reduced to

 

2x^2+7x+8. This can be factored using the quadratic formula(the roots are imaginary since b^2<4ac) where a=2, b=7, and c=8 where:

 

x=(1/2a)*((-b)+/-sqrt(b^2-4ac))

 

x=(1/4)*((-7)+/-sqrt(49-64))

 

x=(1/4)*(-7+/-sqrt(-15))

 

remember that sqrt(-1) = i

 

x=(1/4)*(-7+/-sqrt(15)i)

 

therefore going under the assumption that ?? is a variable just like any other, then 

 

?? =(1/4)*(-7+/-sqrt(15)i)

 

if you find out something different for the ??, please let me know