SOLUTION: Solve using quadratic formula 0.7x^2 = 4.2x + 0.7

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Question 717930: Solve using quadratic formula
0.7x^2 = 4.2x + 0.7
Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
0.7x%5E2+=+4.2x+%2B+0.7
Although it's not required, I prefer to eliminate fractions and decimals (if it's not too hard). With this equation all we have to do is multiply each side by 10:
7x%5E2+=+42x+%2B+7

Before we use the Quadratic Formula, we have to put the equation into standard form, ax%5E2%2Bbx%2Bc=0. Subtracting the entire right side we get:
7x%5E2+-+42x+-+7+=+0

Now we can use the formula:
x+=+%28-%28-42%29+%2B-+sqrt%28%28-42%29%5E2-4%287%29%28-7%29%29%29%2F2%287%29
Simplifying...
x+=+%28-%28-42%29+%2B-+sqrt%281764-4%287%29%28-7%29%29%29%2F2%287%29
x+=+%28-%28-42%29+%2B-+sqrt%281764%2B196%29%29%2F2%287%29
x+=+%28-%28-42%29+%2B-+sqrt%281960%29%29%2F2%287%29
x+=+%2842+%2B-+sqrt%281960%29%29%2F14
x+=+%2842+%2B-+sqrt%284%2A49%2A10%29%29%2F14
x+=+%2842+%2B-+sqrt%284%29%2Asqrt%2849%29%2Asqrt%2810%29%29%2F14
x+=+%2842+%2B-+2%2A7%2Asqrt%2810%29%29%2F14
x+=+%2842+%2B-+14%2Asqrt%2810%29%29%2F14
x+=+%2814%283+%2B-+sqrt%2810%29%29%29%2F14
x+=+%28cross%2814%29%283+%2B-+sqrt%2810%29%29%29%2Fcross%2814%29
x+=+3+%2B-+sqrt%2810%29
which is short for:
x+=+3+%2B+sqrt%2810%29 or x+=+3+-+sqrt%2810%29

P.S. You should get exactly the same answers if you don't bother eliminating the decimals.