Solve the Quadratic Equation: 2x² + x - 10 = 0

Quadratic Formula with Mixed Number Solutions

Solve the following equation:

2x2+x10=0 2x^2+x-10=0

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:04 Identify the coefficients
00:16 Use the roots formula
00:34 Substitute appropriate values according to the given data and solve
01:03 Calculate the square and products
01:17 Calculate the square root of 81
01:30 These are the 2 possible solutions (addition,subtraction)
01:47 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following equation:

2x2+x10=0 2x^2+x-10=0

2

Step-by-step solution

To solve the quadratic equation 2x2+x10=0 2x^2 + x - 10 = 0 , we'll apply the quadratic formula. The equation is in standard form ax2+bx+c=0 ax^2 + bx + c = 0 , where:

  • a=2 a = 2
  • b=1 b = 1
  • c=10 c = -10

Now, substitute these values into the quadratic formula:
x=b±b24ac2a x = \frac{{-b \pm \sqrt{{b^2 - 4ac}}}}{2a}

Step 1: Calculate the discriminant:

b24ac=124×2×(10)=1+80=81 b^2 - 4ac = 1^2 - 4 \times 2 \times (-10) = 1 + 80 = 81

Step 2: Take the square root of the discriminant:

81=9 \sqrt{81} = 9

Step 3: Solve for x x using the quadratic formula:

  • x1=1+94=84=2 x_1 = \frac{{-1 + 9}}{4} = \frac{8}{4} = 2
  • x2=194=104=52=212 x_2 = \frac{{-1 - 9}}{4} = \frac{-10}{4} = -\frac{5}{2} = -2\frac{1}{2}

The solutions to the equation 2x2+x10=0 2x^2 + x - 10 = 0 are x1=2 x_1 = 2 and x2=212 x_2 = -2\frac{1}{2} .

Therefore, the correct choice from the provided options is

x1=212,x2=2 x_1=-2\frac{1}{2}, x_2=2

3

Final Answer

x1=212,x2=2 x_1=-2\frac{1}{2},x_2=2

Key Points to Remember

Essential concepts to master this topic
  • Formula: Use x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} for standard form
  • Discriminant: Calculate b24ac=124(2)(10)=81 b^2 - 4ac = 1^2 - 4(2)(-10) = 81
  • Check: Substitute both solutions back: 2(2)2+210=0 2(2)^2 + 2 - 10 = 0

Common Mistakes

Avoid these frequent errors
  • Sign errors when calculating the discriminant
    Don't forget that 4ac=4(2)(10)=+80 -4ac = -4(2)(-10) = +80 , not -80! Negative times negative equals positive. Always be extra careful with signs when substituting into b24ac b^2 - 4ac .

Practice Quiz

Test your knowledge with interactive questions

a = coefficient of x²

b = coefficient of x

c = coefficient of the constant term


What is the value of \( c \) in the function \( y=-x^2+25x \)?

FAQ

Everything you need to know about this question

Why do we get two different answers for x?

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Quadratic equations create parabolas that can cross the x-axis at two points. Each crossing point gives us a solution, so it's normal to have two values that make the equation true!

What does the discriminant tell us?

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The discriminant b24ac b^2 - 4ac shows what type of solutions you'll get: positive means two real solutions, zero means one solution, and negative means no real solutions.

Can I use factoring instead of the quadratic formula?

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Yes! Try factoring first - it's often faster. For 2x2+x10=0 2x^2 + x - 10 = 0 , look for two numbers that multiply to -20 and add to 1. If factoring seems difficult, the quadratic formula always works!

How do I convert the decimal -2.5 to a mixed number?

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2.5=212 -2.5 = -2\frac{1}{2} because the 0.5 part equals 12 \frac{1}{2} . Remember that mixed numbers show the whole number part separately from the fraction part.

What if my discriminant isn't a perfect square?

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If b24ac \sqrt{b^2 - 4ac} doesn't simplify to a whole number, leave it as a square root in your final answer. For example, 13 \sqrt{13} cannot be simplified further.

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