Question

Joyce is trying to solve the equation y = x^2 − 8x + 7 using the quadratic formula. She has made an error in one of the steps below. Find the step where Joyce went wrong.

Step 1: x = - 8 plus or minus the square root of (8^2 - 4 * 1 * 7) all over 2 * 1.

Step 2: x = - 8 plus or minus the square root of 64 - 28 all over 2 * 1.

Step 3: x = - 8 plus or minus the square root of 36 all over 2 * 1.

Step 4: x = - 8 plus or minus 6 all over 2.

Answer 1

Possible answers are:

step 1

step 2

step 3

step 4

Answer 2

@Sunshine447 do you know quadratic formula?

Answer 3

Not really... I don't remember which one that is...

Answer 4

A standard quadratic equation is of the form
\[ax^2+bx+c=0\]
Its roots are given as
\[x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}\]
What is a, b and c here?

Answer 5

a=1 b=-8 and c=7... I think...

Answer 6

Yeah you're right, now use the quadratic formula to solve for x

Answer 7

x=8 plus or minus the square root of (-8^2-28)
-----------------------------------------
2

Answer 8

is that right???

Answer 9

Almost right
\[x=\frac{-(-8)\pm \sqrt{(-8)^2-4\times 7 \times1 }}{2 \times 1}\]
so we get
\[x=\frac{8\pm \sqrt{64-28 }}{2 }\]
\[x=\frac{8\pm \sqrt{36 }}{2 }\]
Can you solve the rest?