Solve 6b^2+11b+4

$$6 b ^ { 2 } + 11 b + 4$$

Factor

$$\left(2b+1\right)\left(3b+4\right)$$

Solution Steps

Factor the expression by grouping. First, the expression needs to be rewritten as 6b^{2}+pb+qb+4. To find p and q, set up a system to be solved.

$$p+q=11 pq=6\times 4=24$$

Since pq is positive, p and q have the same sign. Since p+q is positive, p and q are both positive. List all such integer pairs that give product 24.

$$1,24 2,12 3,8 4,6$$

Calculate the sum for each pair.

$$1+24=25 2+12=14 3+8=11 4+6=10$$

The solution is the pair that gives sum 11.

$$p=3 q=8$$

Rewrite 6b^{2}+11b+4 as \left(6b^{2}+3b\right)+\left(8b+4\right).

$$\left(6b^{2}+3b\right)+\left(8b+4\right)$$

Factor out 3b in the first and 4 in the second group.

$$3b\left(2b+1\right)+4\left(2b+1\right)$$

Factor out common term 2b+1 by using distributive property.

$$\left(2b+1\right)\left(3b+4\right)$$

Steps Using the Quadratic Formula

Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.

$$6b^{2}+11b+4=0$$

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.

$$b=\frac{-11±\sqrt{11^{2}-4\times 6\times 4}}{2\times 6}$$

Square 11.

$$b=\frac{-11±\sqrt{121-4\times 6\times 4}}{2\times 6}$$

Multiply -4 times 6.

$$b=\frac{-11±\sqrt{121-24\times 4}}{2\times 6}$$

Multiply -24 times 4.

$$b=\frac{-11±\sqrt{121-96}}{2\times 6}$$

Add 121 to -96.

$$b=\frac{-11±\sqrt{25}}{2\times 6}$$

Take the square root of 25.

$$b=\frac{-11±5}{2\times 6}$$

Multiply 2 times 6.

$$b=\frac{-11±5}{12}$$

Now solve the equation b=\frac{-11±5}{12} when ± is plus. Add -11 to 5.

$$b=-\frac{6}{12}$$

Reduce the fraction \frac{-6}{12} to lowest terms by extracting and canceling out 6.

$$b=-\frac{1}{2}$$

Now solve the equation b=\frac{-11±5}{12} when ± is minus. Subtract 5 from -11.

$$b=-\frac{16}{12}$$

Reduce the fraction \frac{-16}{12} to lowest terms by extracting and canceling out 4.

$$b=-\frac{4}{3}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -\frac{1}{2} for x_{1} and -\frac{4}{3} for x_{2}.

$$6b^{2}+11b+4=6\left(b-\left(-\frac{1}{2}\right)\right)\left(b-\left(-\frac{4}{3}\right)\right)$$

Simplify all the expressions of the form p-\left(-q\right) to p+q.

$$6b^{2}+11b+4=6\left(b+\frac{1}{2}\right)\left(b+\frac{4}{3}\right)$$

Add \frac{1}{2} to b by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$6b^{2}+11b+4=6\times \frac{2b+1}{2}\left(b+\frac{4}{3}\right)$$

Add \frac{4}{3} to b by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$6b^{2}+11b+4=6\times \frac{2b+1}{2}\times \frac{3b+4}{3}$$

Multiply \frac{2b+1}{2} times \frac{3b+4}{3} by multiplying numerator times numerator and denominator times denominator. Then reduce the fraction to lowest terms if possible.

$$6b^{2}+11b+4=6\times \frac{\left(2b+1\right)\left(3b+4\right)}{2\times 3}$$

Multiply 2 times 3.

$$6b^{2}+11b+4=6\times \frac{\left(2b+1\right)\left(3b+4\right)}{6}$$

Cancel out 6, the greatest common factor in 6 and 6.

$$6b^{2}+11b+4=\left(2b+1\right)\left(3b+4\right)$$

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.This is achieved by dividing both sides of the equation by 6

$$x ^ 2 +\frac{11}{6}x +\frac{2}{3} = 0$$

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

$$r + s = -\frac{11}{6} rs = \frac{2}{3}$$

Two numbers r and s sum up to -\frac{11}{6} exactly when the average of the two numbers is \frac{1}{2}*-\frac{11}{6} = -\frac{11}{12}. 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-gzdabgg4ehffg0hf.b01.azurefd.net/customsolver/quadraticgraph.png' style='width: 100%;max-width: 700px' /></div>

$$r = -\frac{11}{12} - u s = -\frac{11}{12} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = \frac{2}{3}

$$(-\frac{11}{12} - u) (-\frac{11}{12} + u) = \frac{2}{3}$$

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

$$\frac{121}{144} - u^2 = \frac{2}{3}$$

Simplify the expression by subtracting \frac{121}{144} on both sides

$$-u^2 = \frac{2}{3}-\frac{121}{144} = -\frac{25}{144}$$

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

$$u^2 = \frac{25}{144} u = \pm\sqrt{\frac{25}{144}} = \pm \frac{5}{12}$$

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

$$r =-\frac{11}{12} - \frac{5}{12} = -1.333 s = -\frac{11}{12} + \frac{5}{12} = -0.500$$

Evaluate

$$\left(2b+1\right)\left(3b+4\right)$$