SOLUTION: Step by step solving of the following equation: {{{ ((1/4)*x)+(2*sqrt(x))+15=x }}}

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Step by step solving of the following equation: {{{ ((1/4)*x)+(2*sqrt(x))+15=x }}}      Log On


   



Question 1087038: Step by step solving of the following equation:
+%28%281%2F4%29%2Ax%29%2B%282%2Asqrt%28x%29%29%2B15=x+

Found 2 solutions by ikleyn, Alan3354:
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
.
There is nothing easier than it.

Introduce new variable y = sqrt%28x%29.   Then y%5E2 = x.


Then your equation takes the form

%281%2F4%29y%5E2+%2B+2y+%2B+15 = y%5E2  ====>  (Multiply both sides by 4)  ====>

y%5E2+%2B+8y+%2B+60 = 4y%5E2  ====>

3y%5E2+-+8y+-+60 = 0  ====>  (apply the quadratic formula)  ====>

y%5B1%2C2%5D = %288+%2B-+sqrt%288%5E2+%2B+4%2A3%2A60%29%29%2F%282%2A3%29 = %288+%2B-+sqrt%28784%29%29%2F6 = %288+%2B-+28%29%2F6.


1)  y%5B1%5D = %288+%2B+28%29%2F6 = 36%2F6 = 6  ====>  x%5B1%5D = 6%5E2 = 36;


2)  y%5B2%5D = %288+-+28%29%2F6 = -20%2F6 = -10%2F3  ====>  x%5B2%5D = %28-10%2F3%29%5E2 = 100%2F9.


Check each root. You will see that x = 36 is valid solution, while x = 100%2F9 is EXTRANEOUS.


Answer.  The solution (and the only solution) is  x = 36.

Illustration:



Plot y = %281%2F4%29%2Ax%2B2%2Asqrt%28x%29%2B15 (the left side of the original equation; red line) and y = x (the right side; green).



Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
+%281%2F4%29%2Ax%2B2%2Asqrt%28x%29+%2B+15+=+x+
2%2Asqrt%28x%29+=+3x%2F4+-+15+
8sqrt%28x%29+=+3x+-+60
Square
64x+=+9x%5E2+-+360x+%2B+3600
9x%5E2+-+424x+%2B+3600+=+0
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Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 9x%5E2%2B-424x%2B3600+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%28-424%29%5E2-4%2A9%2A3600=50176.

Discriminant d=50176 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--424%2B-sqrt%28+50176+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-424%29%2Bsqrt%28+50176+%29%29%2F2%5C9+=+36
x%5B2%5D+=+%28-%28-424%29-sqrt%28+50176+%29%29%2F2%5C9+=+11.1111111111111

Quadratic expression 9x%5E2%2B-424x%2B3600 can be factored:
9x%5E2%2B-424x%2B3600+=+%28x-36%29%2A%28x-11.1111111111111%29
Again, the answer is: 36, 11.1111111111111. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+9%2Ax%5E2%2B-424%2Ax%2B3600+%29

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x = 36
x = 100/9 *** extraneous, not a solution