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1000=850+105x+2x^{2}
Use the distributive property to multiply 10+x by 85+2x and combine like terms.
850+105x+2x^{2}=1000
Swap sides so that all variable terms are on the left hand side.
850+105x+2x^{2}-1000=0
Subtract 1000 from both sides.
-150+105x+2x^{2}=0
Subtract 1000 from 850 to get -150.
2x^{2}+105x-150=0
All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. The quadratic formula gives two solutions, one when ± is addition and one when it is subtraction.
x=\frac{-105±\sqrt{105^{2}-4\times 2\left(-150\right)}}{2\times 2}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 2 for a, 105 for b, and -150 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-105±\sqrt{11025-4\times 2\left(-150\right)}}{2\times 2}
Square 105.
x=\frac{-105±\sqrt{11025-8\left(-150\right)}}{2\times 2}
Multiply -4 times 2.
x=\frac{-105±\sqrt{11025+1200}}{2\times 2}
Multiply -8 times -150.
x=\frac{-105±\sqrt{12225}}{2\times 2}
Add 11025 to 1200.
x=\frac{-105±5\sqrt{489}}{2\times 2}
Take the square root of 12225.
x=\frac{-105±5\sqrt{489}}{4}
Multiply 2 times 2.
x=\frac{5\sqrt{489}-105}{4}
Now solve the equation x=\frac{-105±5\sqrt{489}}{4} when ± is plus. Add -105 to 5\sqrt{489}.
x=\frac{-5\sqrt{489}-105}{4}
Now solve the equation x=\frac{-105±5\sqrt{489}}{4} when ± is minus. Subtract 5\sqrt{489} from -105.
x=\frac{5\sqrt{489}-105}{4} x=\frac{-5\sqrt{489}-105}{4}
The equation is now solved.
1000=850+105x+2x^{2}
Use the distributive property to multiply 10+x by 85+2x and combine like terms.
850+105x+2x^{2}=1000
Swap sides so that all variable terms are on the left hand side.
105x+2x^{2}=1000-850
Subtract 850 from both sides.
105x+2x^{2}=150
Subtract 850 from 1000 to get 150.
2x^{2}+105x=150
Quadratic equations such as this one can be solved by completing the square. In order to complete the square, the equation must first be in the form x^{2}+bx=c.
\frac{2x^{2}+105x}{2}=\frac{150}{2}
Divide both sides by 2.
x^{2}+\frac{105}{2}x=\frac{150}{2}
Dividing by 2 undoes the multiplication by 2.
x^{2}+\frac{105}{2}x=75
Divide 150 by 2.
x^{2}+\frac{105}{2}x+\left(\frac{105}{4}\right)^{2}=75+\left(\frac{105}{4}\right)^{2}
Divide \frac{105}{2}, the coefficient of the x term, by 2 to get \frac{105}{4}. Then add the square of \frac{105}{4} to both sides of the equation. This step makes the left hand side of the equation a perfect square.
x^{2}+\frac{105}{2}x+\frac{11025}{16}=75+\frac{11025}{16}
Square \frac{105}{4} by squaring both the numerator and the denominator of the fraction.
x^{2}+\frac{105}{2}x+\frac{11025}{16}=\frac{12225}{16}
Add 75 to \frac{11025}{16}.
\left(x+\frac{105}{4}\right)^{2}=\frac{12225}{16}
Factor x^{2}+\frac{105}{2}x+\frac{11025}{16}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.
\sqrt{\left(x+\frac{105}{4}\right)^{2}}=\sqrt{\frac{12225}{16}}
Take the square root of both sides of the equation.
x+\frac{105}{4}=\frac{5\sqrt{489}}{4} x+\frac{105}{4}=-\frac{5\sqrt{489}}{4}
Simplify.
x=\frac{5\sqrt{489}-105}{4} x=\frac{-5\sqrt{489}-105}{4}
Subtract \frac{105}{4} from both sides of the equation.