Solve for x
x=3
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x^{2}-10x+21=0
Variable x cannot be equal to any of the values \frac{1}{2},7 since division by zero is not defined. Multiply both sides of the equation by \left(x-7\right)\left(2x-1\right).
a+b=-10 ab=21
To solve the equation, factor x^{2}-10x+21 using formula x^{2}+\left(a+b\right)x+ab=\left(x+a\right)\left(x+b\right). To find a and b, set up a system to be solved.
-1,-21 -3,-7
Since ab is positive, a and b have the same sign. Since a+b is negative, a and b are both negative. List all such integer pairs that give product 21.
-1-21=-22 -3-7=-10
Calculate the sum for each pair.
a=-7 b=-3
The solution is the pair that gives sum -10.
\left(x-7\right)\left(x-3\right)
Rewrite factored expression \left(x+a\right)\left(x+b\right) using the obtained values.
x=7 x=3
To find equation solutions, solve x-7=0 and x-3=0.
x=3
Variable x cannot be equal to 7.
x^{2}-10x+21=0
Variable x cannot be equal to any of the values \frac{1}{2},7 since division by zero is not defined. Multiply both sides of the equation by \left(x-7\right)\left(2x-1\right).
a+b=-10 ab=1\times 21=21
To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as x^{2}+ax+bx+21. To find a and b, set up a system to be solved.
-1,-21 -3,-7
Since ab is positive, a and b have the same sign. Since a+b is negative, a and b are both negative. List all such integer pairs that give product 21.
-1-21=-22 -3-7=-10
Calculate the sum for each pair.
a=-7 b=-3
The solution is the pair that gives sum -10.
\left(x^{2}-7x\right)+\left(-3x+21\right)
Rewrite x^{2}-10x+21 as \left(x^{2}-7x\right)+\left(-3x+21\right).
x\left(x-7\right)-3\left(x-7\right)
Factor out x in the first and -3 in the second group.
\left(x-7\right)\left(x-3\right)
Factor out common term x-7 by using distributive property.
x=7 x=3
To find equation solutions, solve x-7=0 and x-3=0.
x=3
Variable x cannot be equal to 7.
x^{2}-10x+21=0
Variable x cannot be equal to any of the values \frac{1}{2},7 since division by zero is not defined. Multiply both sides of the equation by \left(x-7\right)\left(2x-1\right).
x=\frac{-\left(-10\right)±\sqrt{\left(-10\right)^{2}-4\times 21}}{2}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, -10 for b, and 21 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-\left(-10\right)±\sqrt{100-4\times 21}}{2}
Square -10.
x=\frac{-\left(-10\right)±\sqrt{100-84}}{2}
Multiply -4 times 21.
x=\frac{-\left(-10\right)±\sqrt{16}}{2}
Add 100 to -84.
x=\frac{-\left(-10\right)±4}{2}
Take the square root of 16.
x=\frac{10±4}{2}
The opposite of -10 is 10.
x=\frac{14}{2}
Now solve the equation x=\frac{10±4}{2} when ± is plus. Add 10 to 4.
x=7
Divide 14 by 2.
x=\frac{6}{2}
Now solve the equation x=\frac{10±4}{2} when ± is minus. Subtract 4 from 10.
x=3
Divide 6 by 2.
x=7 x=3
The equation is now solved.
x=3
Variable x cannot be equal to 7.
x^{2}-10x+21=0
Variable x cannot be equal to any of the values \frac{1}{2},7 since division by zero is not defined. Multiply both sides of the equation by \left(x-7\right)\left(2x-1\right).
x^{2}-10x=-21
Subtract 21 from both sides. Anything subtracted from zero gives its negation.
x^{2}-10x+\left(-5\right)^{2}=-21+\left(-5\right)^{2}
Divide -10, the coefficient of the x term, by 2 to get -5. Then add the square of -5 to both sides of the equation. This step makes the left hand side of the equation a perfect square.
x^{2}-10x+25=-21+25
Square -5.
x^{2}-10x+25=4
Add -21 to 25.
\left(x-5\right)^{2}=4
Factor x^{2}-10x+25. 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-5\right)^{2}}=\sqrt{4}
Take the square root of both sides of the equation.
x-5=2 x-5=-2
Simplify.
x=7 x=3
Add 5 to both sides of the equation.
x=3
Variable x cannot be equal to 7.
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