Solve y^2+50y+336=0

$$y ^ { 2 } + 50 y + 336 = 0$$

Solve for y

$$y=-42$$

$$y=-8$$

Steps Using Factoring

To solve the equation, factor y^{2}+50y+336 using formula y^{2}+\left(a+b\right)y+ab=\left(y+a\right)\left(y+b\right). To find a and b, set up a system to be solved.

$$a+b=50 ab=336$$

Since ab is positive, a and b have the same sign. Since a+b is positive, a and b are both positive. List all such integer pairs that give product 336.

$$1,336 2,168 3,112 4,84 6,56 7,48 8,42 12,28 14,24 16,21$$

Calculate the sum for each pair.

$$1+336=337 2+168=170 3+112=115 4+84=88 6+56=62 7+48=55 8+42=50 12+28=40 14+24=38 16+21=37$$

The solution is the pair that gives sum 50.

$$a=8 b=42$$

Rewrite factored expression \left(y+a\right)\left(y+b\right) using the obtained values.

$$\left(y+8\right)\left(y+42\right)$$

To find equation solutions, solve y+8=0 and y+42=0.

$$y=-8 y=-42$$

Steps Using Factoring By Grouping

To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as y^{2}+ay+by+336. To find a and b, set up a system to be solved.

$$a+b=50 ab=1\times 336=336$$

Since ab is positive, a and b have the same sign. Since a+b is positive, a and b are both positive. List all such integer pairs that give product 336.

$$1,336 2,168 3,112 4,84 6,56 7,48 8,42 12,28 14,24 16,21$$

Calculate the sum for each pair.

$$1+336=337 2+168=170 3+112=115 4+84=88 6+56=62 7+48=55 8+42=50 12+28=40 14+24=38 16+21=37$$

The solution is the pair that gives sum 50.

$$a=8 b=42$$

Rewrite y^{2}+50y+336 as \left(y^{2}+8y\right)+\left(42y+336\right).

$$\left(y^{2}+8y\right)+\left(42y+336\right)$$

Factor out y in the first and 42 in the second group.

$$y\left(y+8\right)+42\left(y+8\right)$$

Factor out common term y+8 by using distributive property.

$$\left(y+8\right)\left(y+42\right)$$

To find equation solutions, solve y+8=0 and y+42=0.

$$y=-8 y=-42$$

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.

$$y^{2}+50y+336=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, 50 for b, and 336 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$y=\frac{-50±\sqrt{50^{2}-4\times 336}}{2}$$

Square 50.

$$y=\frac{-50±\sqrt{2500-4\times 336}}{2}$$

Multiply -4 times 336.

$$y=\frac{-50±\sqrt{2500-1344}}{2}$$

Add 2500 to -1344.

$$y=\frac{-50±\sqrt{1156}}{2}$$

Take the square root of 1156.

$$y=\frac{-50±34}{2}$$

Now solve the equation y=\frac{-50±34}{2} when ± is plus. Add -50 to 34.

$$y=-\frac{16}{2}$$

Divide -16 by 2.

$$y=-8$$

Now solve the equation y=\frac{-50±34}{2} when ± is minus. Subtract 34 from -50.

$$y=-\frac{84}{2}$$

Divide -84 by 2.

$$y=-42$$

The equation is now solved.

$$y=-8 y=-42$$

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.

$$y^{2}+50y+336=0$$

Subtract 336 from both sides of the equation.

$$y^{2}+50y+336-336=-336$$

Subtracting 336 from itself leaves 0.

$$y^{2}+50y=-336$$

Divide 50, the coefficient of the x term, by 2 to get 25. Then add the square of 25 to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$y^{2}+50y+25^{2}=-336+25^{2}$$

Square 25.

$$y^{2}+50y+625=-336+625$$

Add -336 to 625.

$$y^{2}+50y+625=289$$

Factor y^{2}+50y+625. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(y+25\right)^{2}=289$$

Take the square root of both sides of the equation.

$$\sqrt{\left(y+25\right)^{2}}=\sqrt{289}$$

Simplify.

$$y+25=17 y+25=-17$$

Subtract 25 from both sides of the equation.

$$y=-8 y=-42$$

Steps Using Direct Factoring Method

Quadratic equations such as this one can be solved by a new direct factoring method that does not require guess work. To use the direct factoring method, the equation must be in the form x^2+Bx+C=0.

$$x ^ 2 +50x +336 = 0$$

Let r and s be the factors for the quadratic equation such that x^2+Bx+C=(x−r)(x−s) where sum of factors (r+s)=−B and the product of factors rs = C

$$r + s = -50 rs = 336$$

Two numbers r and s sum up to -50 exactly when the average of the two numbers is \frac{1}{2}*-50 = -25. You can also see that the midpoint of r and s corresponds to the axis of symmetry of the parabola represented by the quadratic equation y=x^2+Bx+C. The values of r and s are equidistant from the center by an unknown quantity u. Express r and s with respect to variable u. <div style='padding: 8px'><img src='https://opalmath.azureedge.net/customsolver/quadraticgraph.png' style='width: 100%;max-width: 700px' /></div>

$$r = -25 - u s = -25 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 336

$$(-25 - u) (-25 + u) = 336$$

Simplify by expanding (a -b) (a + b) = a^2 – b^2

$$625 - u^2 = 336$$

Simplify the expression by subtracting 625 on both sides

$$-u^2 = 336-625 = -289$$

Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u

$$u^2 = 289 u = \pm\sqrt{289} = \pm 17$$

The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.

$$r =-25 - 17 = -42 s = -25 + 17 = -8$$