2x^2-6x-80=-এর সমাধান করুন

$$2 x ^ { 2 } - 6 x - 80 =$$

Factor

$$2\left(x-8\right)\left(x+5\right)$$

Solution Steps

Factor out 2.

$$2\left(x^{2}-3x-40\right)$$

Consider x^{2}-3x-40. Factor the expression by grouping. First, the expression needs to be rewritten as x^{2}+ax+bx-40. To find a and b, set up a system to be solved.

$$a+b=-3 ab=1\left(-40\right)=-40$$

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 -40.

$$1,-40 2,-20 4,-10 5,-8$$

Calculate the sum for each pair.

$$1-40=-39 2-20=-18 4-10=-6 5-8=-3$$

The solution is the pair that gives sum -3.

$$a=-8 b=5$$

Rewrite x^{2}-3x-40 as \left(x^{2}-8x\right)+\left(5x-40\right).

$$\left(x^{2}-8x\right)+\left(5x-40\right)$$

Factor out x in the first and 5 in the second group.

$$x\left(x-8\right)+5\left(x-8\right)$$

Factor out common term x-8 by using distributive property.

$$\left(x-8\right)\left(x+5\right)$$

Rewrite the complete factored expression.

$$2\left(x-8\right)\left(x+5\right)$$

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.

$$2x^{2}-6x-80=0$$

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.

$$x=\frac{-\left(-6\right)±\sqrt{\left(-6\right)^{2}-4\times 2\left(-80\right)}}{2\times 2}$$

Square -6.

$$x=\frac{-\left(-6\right)±\sqrt{36-4\times 2\left(-80\right)}}{2\times 2}$$

Multiply -4 times 2.

$$x=\frac{-\left(-6\right)±\sqrt{36-8\left(-80\right)}}{2\times 2}$$

Multiply -8 times -80.

$$x=\frac{-\left(-6\right)±\sqrt{36+640}}{2\times 2}$$

Add 36 to 640.

$$x=\frac{-\left(-6\right)±\sqrt{676}}{2\times 2}$$

Take the square root of 676.

$$x=\frac{-\left(-6\right)±26}{2\times 2}$$

The opposite of -6 is 6.

$$x=\frac{6±26}{2\times 2}$$

Multiply 2 times 2.

$$x=\frac{6±26}{4}$$

Now solve the equation x=\frac{6±26}{4} when ± is plus. Add 6 to 26.

$$x=\frac{32}{4}$$

Divide 32 by 4.

$$x=8$$

Now solve the equation x=\frac{6±26}{4} when ± is minus. Subtract 26 from 6.

$$x=-\frac{20}{4}$$

Divide -20 by 4.

$$x=-5$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute 8 for x_{1} and -5 for x_{2}.

$$2x^{2}-6x-80=2\left(x-8\right)\left(x-\left(-5\right)\right)$$

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

$$2x^{2}-6x-80=2\left(x-8\right)\left(x+5\right)$$

Evaluate

$$2\left(x-8\right)\left(x+5\right)$$