Question

Complete the square:

Y:x^2-8x+21

Someone plz help.

Answer 1

1. Insure the coefficient of the squared term is 1, this case it is.
2. Compute 1/2 the value of the coefficient of the x term. 1/2 of 8 is 4.
3. Square this. Get 16 Now add this to the equation:
\[x ^{2}-8x + 16 +21= 16\]
4. Subtract 21 from both sides getting \[x ^{2}-4x + 16 = -5\]
5. Express the left as a square \[(x - 4)^{2}=-5\]
6. Take the square root of both sides. \[x - 4 = \sqrt{-5}\]
7. Solve getting\[x = 4\pm \sqrt{-5}\]
There you are with two comples roots.

Answer 2

Please correct step 4. to read as:\[x ^{2}-8x +16 = -5\]