SOLUTION: I am trying to solve an equation by factoring. The equation is: x^2/2 + x/20 = 10 What I have done is cleared the denominators and ended up with: 10x^2 + x = 10

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: I am trying to solve an equation by factoring. The equation is: x^2/2 + x/20 = 10 What I have done is cleared the denominators and ended up with: 10x^2 + x = 10       Log On


   



Question 667139: I am trying to solve an equation by factoring. The equation is:
x^2/2 + x/20 = 10
What I have done is cleared the denominators and ended up with:
10x^2 + x = 10
Then I moved the 10 to the left side of the equation and ended up with:
10x^2 + x -10 = 0
I am stuck and cannot factor: 10x^2 + x -10
The answer in the back of the book is: {2/5, -1/2}, but am not sure how to get to this answer without successfully factoring first.
In an attempt to factor, I multiplied the first and last coefficients and came up with -100. There are no numbers that when multiplied together equal -100 and also equal the middle coefficient of 1 when added together.
Please help.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+%28x%5E2%29%2F2+%2B+x%2F20+=+10+
You are not simply changing the appearance
of the fractions on the left side. This would be
the case if you did:
+%2810%2F10%29%2A%28%28x%5E2%29%2F2%29+%2B+x%2F20+=+10+
Note that you haven't really changed the value
of the left side
+%28+10x%5E2+%29%2F+20+%2B+x%2F20+=+200%2F20+
Now you can multiply through by +20+
+10x%5E2+%2B+x+=+200+
--------------------------
What you wanted to do was multiply both sides by +20+
+%28x%5E2%29%2F2+%2B+x%2F20+=+10+
+10x%5E2+%2B+x+=+200+
same answer
+10x%5E2+%2B+x+-+200+=+0+
You can use the quadratic formula
+x+=+%28-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+10+
+b+=+1+
+c+=+-200+
+x+=+%28-1+%2B-+sqrt%28+1%5E2+-+4%2A10%2A%28-200%29+%29%29+%2F+%282%2A10%29+
+x+=+%28-1+%2B-+sqrt%28+1+%2B+8000+%29%29+%2F+20+
+x+=+%28-1+%2B-+sqrt%28+8001+%29%29+%2F+20+
+x+=+%28+-1+%2B+89.4483+%29+%2F+20+
+x+=+88.4483+%2F+20+
+x+=+4.4224+
and
+x+=+%28+-1+-+89.4483+%29+%2F+20+
+x+=+%28+-90.4483+%29+%2F+20+
+x+=+-4.5224+
check:
+%28+x+-+4.4224+%29%2A%28+x+%2B+4.5224+%29+
+x%5E2+%2B+.1x+-+20+
Multiply both sides by +1%2F2+
+%28x%5E2%29%2F2+%2B+x%2F20+-+10+=+0+
+%28x%5E2%29%2F2+%2B+x%2F20+=+10+
OK
Why does the book disagree? I don't know