Solve 49x^2-14x=8

$$49 x ^ { 2 } - 14 x = 8$$

Solve for x

$$x=-\frac{2}{7}\approx -0.285714286$$

$$x=\frac{4}{7}\approx 0.571428571$$

Steps Using Factoring By Grouping

Subtract 8 from both sides.

$$49x^{2}-14x-8=0$$

To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as 49x^{2}+ax+bx-8. To find a and b, set up a system to be solved.

$$a+b=-14 ab=49\left(-8\right)=-392$$

Since ab is negative, a and b have the opposite signs. Since a+b is negative, the negative number has greater absolute value than the positive. List all such integer pairs that give product -392.

$$1,-392 2,-196 4,-98 7,-56 8,-49 14,-28$$

Calculate the sum for each pair.

$$1-392=-391 2-196=-194 4-98=-94 7-56=-49 8-49=-41 14-28=-14$$

The solution is the pair that gives sum -14.

$$a=-28 b=14$$

Rewrite 49x^{2}-14x-8 as \left(49x^{2}-28x\right)+\left(14x-8\right).

$$\left(49x^{2}-28x\right)+\left(14x-8\right)$$

Factor out 7x in the first and 2 in the second group.

$$7x\left(7x-4\right)+2\left(7x-4\right)$$

Factor out common term 7x-4 by using distributive property.

$$\left(7x-4\right)\left(7x+2\right)$$

To find equation solutions, solve 7x-4=0 and 7x+2=0.

$$x=\frac{4}{7} x=-\frac{2}{7}$$

Steps Using the Quadratic Formula

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.

$$49x^{2}-14x=8$$

Subtract 8 from both sides of the equation.

$$49x^{2}-14x-8=8-8$$

Subtracting 8 from itself leaves 0.

$$49x^{2}-14x-8=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 49 for a, -14 for b, and -8 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-14\right)±\sqrt{\left(-14\right)^{2}-4\times 49\left(-8\right)}}{2\times 49}$$

Square -14.

$$x=\frac{-\left(-14\right)±\sqrt{196-4\times 49\left(-8\right)}}{2\times 49}$$

Multiply -4 times 49.

$$x=\frac{-\left(-14\right)±\sqrt{196-196\left(-8\right)}}{2\times 49}$$

Multiply -196 times -8.

$$x=\frac{-\left(-14\right)±\sqrt{196+1568}}{2\times 49}$$

Add 196 to 1568.

$$x=\frac{-\left(-14\right)±\sqrt{1764}}{2\times 49}$$

Take the square root of 1764.

$$x=\frac{-\left(-14\right)±42}{2\times 49}$$

The opposite of -14 is 14.

$$x=\frac{14±42}{2\times 49}$$

Multiply 2 times 49.

$$x=\frac{14±42}{98}$$

Now solve the equation x=\frac{14±42}{98} when ± is plus. Add 14 to 42.

$$x=\frac{56}{98}$$

Reduce the fraction \frac{56}{98} to lowest terms by extracting and canceling out 14.

$$x=\frac{4}{7}$$

Now solve the equation x=\frac{14±42}{98} when ± is minus. Subtract 42 from 14.

$$x=-\frac{28}{98}$$

Reduce the fraction \frac{-28}{98} to lowest terms by extracting and canceling out 14.

$$x=-\frac{2}{7}$$

The equation is now solved.

$$x=\frac{4}{7} x=-\frac{2}{7}$$

Steps for Completing the Square

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.

$$49x^{2}-14x=8$$

Divide both sides by 49.

$$\frac{49x^{2}-14x}{49}=\frac{8}{49}$$

Dividing by 49 undoes the multiplication by 49.

$$x^{2}+\left(-\frac{14}{49}\right)x=\frac{8}{49}$$

Reduce the fraction \frac{-14}{49} to lowest terms by extracting and canceling out 7.

$$x^{2}-\frac{2}{7}x=\frac{8}{49}$$

Divide -\frac{2}{7}, the coefficient of the x term, by 2 to get -\frac{1}{7}. Then add the square of -\frac{1}{7} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{2}{7}x+\left(-\frac{1}{7}\right)^{2}=\frac{8}{49}+\left(-\frac{1}{7}\right)^{2}$$

Square -\frac{1}{7} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{2}{7}x+\frac{1}{49}=\frac{8+1}{49}$$

Add \frac{8}{49} to \frac{1}{49} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}-\frac{2}{7}x+\frac{1}{49}=\frac{9}{49}$$

Factor x^{2}-\frac{2}{7}x+\frac{1}{49}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{1}{7}\right)^{2}=\frac{9}{49}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{1}{7}\right)^{2}}=\sqrt{\frac{9}{49}}$$

Simplify.

$$x-\frac{1}{7}=\frac{3}{7} x-\frac{1}{7}=-\frac{3}{7}$$

Add \frac{1}{7} to both sides of the equation.

$$x=\frac{4}{7} x=-\frac{2}{7}$$