Find the Leading Coefficient in -x² + 7x - 9: Identifying Value of a

Quadratic Coefficients with Negative Leading Terms

Determine the value of the coefficient a a in the following equation:

x2+7x9 -x^2+7x-9

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the coefficient A in the equation
00:03 We'll use the formula for representing a quadratic equation
00:11 We can see that coefficient A is of X squared
00:18 Let's compare the formula to our equation and find A
00:21 Every number is essentially multiplied by 1
00:24 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

Determine the value of the coefficient a a in the following equation:

x2+7x9 -x^2+7x-9

2

Step-by-step solution

The quadratic equation in the problem is already arranged (meaning all terms are on one side and 0 on the other side), so let's proceed to answer the question asked:

The question asked in the problem - What is the value of the coefficienta a in the equation?

Let's recall the definitions of coefficients in solving quadratic equations and the roots formula:

The rule states that the roots of an equation of the form:

ax2+bx+c=0 ax^2+bx+c=0 are:

x1,2=b±b24ac2a x_{1,2}=\frac{-b\pm\sqrt{b^2-4ac}}{2a}

That is the coefficient a a is the coefficient of the quadratic term (meaning the term with the second power)- x2 x^2 Let's examine the equation in the problem:

x2+7x9=0 -x^2+7x-9 =0

Remember that the minus sign before the quadratic term means multiplication by: 1 -1 , therefore- we can write the equation as:

1x2+7x9=0 -1\cdot x^2+7x-9 =0

The number that multiplies the x2 x^2 , is 1 -1 hence we identify that the coefficient of the quadratic term is the number 1 -1 ,

Therefore the correct answer is A.

3

Final Answer

-1

Key Points to Remember

Essential concepts to master this topic
  • Standard Form: In ax2+bx+c=0 ax^2 + bx + c = 0 , coefficient a multiplies x2 x^2
  • Technique: Rewrite x2 -x^2 as 1x2 -1 \cdot x^2 to identify a = -1
  • Check: Verify a is the number multiplying the highest power term ✓

Common Mistakes

Avoid these frequent errors
  • Confusing the leading coefficient with other coefficients
    Don't identify coefficient a as 7 or -9 from the other terms = wrong quadratic formula application! The coefficient a must be the number multiplying x². Always identify a as the coefficient of the term with the highest power.

Practice Quiz

Test your knowledge with interactive questions

What is the value of the coefficient \( b \) in the equation below?

\( 3x^2+8x-5 \)

FAQ

Everything you need to know about this question

Why is the coefficient -1 and not just 1?

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The negative sign in front of x2 x^2 means we're multiplying by -1. Think of x2 -x^2 as (1)×x2 (-1) \times x^2 , so a = -1.

What if there's no number in front of x²?

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When you see just x2 x^2 with no visible number, the coefficient is 1. It's like writing 1x2 1 \cdot x^2 but we don't show the 1.

How do I remember which coefficient is which?

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Use the pattern ax2+bx+c ax^2 + bx + c : a goes with x2 x^2 , b goes with x x , and c is the constant (no variable).

Does the order of terms matter?

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No! Whether you write x2+7x9 -x^2 + 7x - 9 or 7xx29 7x - x^2 - 9 , the coefficient of x2 x^2 is still -1.

Why is this important for solving quadratic equations?

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The coefficient a is crucial for the quadratic formula: x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} . Using the wrong value gives completely wrong solutions!

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