Question

Which two equations would be most appropriately solved by using the quadratic formula?

Select each correct answer.




(xâ1)^2=4

0.25x^2+0.8xâ8=0

3x^2â4x=15

(xâ6)(x+9)=0

Answer 1

Answer: second and third equations, dear.

Answer 2

Remember that quadratic formula:
`x= \frac{-b(+/-) \sqrt{b^(2)-4ac} }{2a}` is used to solve quadratic equations of the form
`ax^(2)+bx+c`.

Four our problem, the first one,
`(x-1)^2=4`, is not in the form
`ax^(2)+bx+c`. So is not a good idea to use the quadratic formula for this one.

The second one,
`0.25x^(2)+0.8x-8=0`, is in the correct form. Notice that in this equation
`a=0.25`,
`b=0.8`, and
`c=-8`. It would be appropriate to use the quadratic formula to solve this one.

The third one,
`3x^(2)-4x=15`, can be expressed as:
`3x^(2)-4x-15=0`. This equation is also in the correct form. Here
`a=3`,
`b=-4`, and
`c=-15`. It would be appropriate to use the quadratic formula to solve this one.

The fourth one,
`(x-6)(x+6)=0`, is not in the form
`ax^(2)+bx+c`. So is not a good idea to use the quadratic formula for this one.

We can conclude that you should use the quadratic formula to solve the second and third equations.