SOLUTION: Complete the square and solve for x -4x^2-3x+1=0

Algebra ->  Average -> SOLUTION: Complete the square and solve for x -4x^2-3x+1=0      Log On


   



Question 778861: Complete the square and solve for x
-4x^2-3x+1=0

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!

-4x²-3x+1 = 0

Make the leading term positive by multiplying by -1

4x²+3x-1 = 0

Get the -1 off the left side by adding 1 to both sides:

4x²+3x = 1

Divide every number through by 4

4%2F4x²+3%2F4x = 1%2F4

x²+3%2F4x = 1%2F4

1. Multiply the coefficient  of x, 3%2F4 by 1%2F2, getting 3%2F8
2. Square 3%2F8, getting %283%2F8%29%5E2 = 9%2F64
3. Add 9%2F64 to both sides:

x²+3%2F4x+9%2F64 = 1%2F4+9%2F64

The left side will now factor 
as a square: x²+3%2F4x+9%2F64 = (x+3%2F8)(x+3%2F8) = (x+3%2F8)²
Combine the fractions on the right by getting a LCD of 64: 1%2F4+9%2F64 = 16%2F64+9%2F64 = 25%2F64

(x+3%2F8)² = 25%2F64

take square roots of both sides:

sqrt%28%28x%2B3%2F8%29%5E2%29%22%22=%22%22%22%22+%2B-+sqrt%2825%2F64%29

(x+3%2F8) = %22%22+%2B-+5%2F8

Add -3%2F8} to both sides:

x = -3%2F8+%2B-+5%2F8

Using the + :  x = -3%2F8+%2B+5%2F8 = 2%2F8 = 1%2F4

Using the - :  x = -3%2F8+-+5%2F8 = %28-8%29%2F8 = -1

Solutions: 1%2F4 and -1

----------------------------------

It could have been done by factoring:

-4x²-3x+1 = 0

Make the leading term positive by multiplying by -1

4x²+3x-1 = 0

(4x-1)(x+1) = 0

4x-1 = 0;  x+1 = 0
  4x = 1     x = -1
   x = 1%2F4

Edwin