Chapter 5: Problem 60
Evaluate polynomial for \(x=3\) and for \(x=-3\). \(-3 x^{3}+7 x^{2}-4 x-8\)
Short Answer
Expert verified
For x=3, the value is -38. For x=-3, the value is 148.
Step by step solution
01
- Substitute x=3 into the polynomial
Start by substituting the value of x=3 into the polynomial \(-3 x^{3}+7 x^{2}-4 x-8\). This results in \(-3(3)^3 + 7(3)^2 - 4(3) - 8\).
02
- Calculate each term for x=3
Calculate each term separately:\(-3(3)^3 = -3(27) = -81\), \(7(3)^2 = 7(9) = 63\), \(-4(3) = -12\),\(-8 = -8\).
03
- Add the terms for x=3
Sum up all the terms for x=3: \(-81 + 63 - 12 - 8 = -38\).
04
- Substitute x=-3 into the polynomial
Now substitute the value of x=-3 into the polynomial \(-3 x^{3}+7 x^{2}-4 x-8\). This results in \(-3(-3)^3 + 7(-3)^2 - 4(-3) - 8\).
05
- Calculate each term for x=-3
Calculate each term separately:\(-3(-3)^3 = -3(-27) = 81\), \(7(-3)^2 = 7(9) = 63\), \(-4(-3) = 12\),\(-8 = -8\).
06
- Add the terms for x=-3
Sum up all the terms for x=-3: \(81 + 63 + 12 - 8 = 148\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
substitute values in polynomials
To evaluate a polynomial, we need to substitute the variable with a specific value. This means replacing every instance of the variable in the polynomial with the given number.
For instance, given the polynomial \(-3 x^{3}+7 x^{2}-4 x-8\) and the task to evaluate it for \(x=3\):
For instance, given the polynomial \(-3 x^{3}+7 x^{2}-4 x-8\) and the task to evaluate it for \(x=3\):
- Replace every x with 3.
- Substitute values directly into the polynomial equation: \(-3(3)^3 + 7(3)^2 - 4(3) - 8\).
polynomial terms
Polynomials are composed of different terms, each term being a product of a number (coefficient) and a variable raised to a power. For example, in the polynomial \(-3x^3 + 7x^2 - 4x - 8\):
- \(-3x^3\) is the term with x cubed and a coefficient of -3
- \(7x^2\) is the term with x squared and a coefficient of 7
- \(-4x\) is the linear term with a coefficient of -4
- \(-8\) is the constant term
simplify expressions
Once we've substituted the value into the polynomial, the next step is to simplify the expression. This involves:
- Calculating the power of each term first. For instance, \(3^3 = 27\) and \((-3)^3 = -27\).
- Multiplying each result by its coefficient, such as \(-3(27) = -81\).
- Adding or subtracting the results of each term to get the final value.
algebraic operations
Algebra involves several operations that help in simplifying polynomials:
- Addition & Subtraction: In our polynomial, after finding the value of each term, we add or subtract them to get the final result. For x=3, we perform -81 + 63 - 12 - 8.
- Multiplication: This is required when calculating the coefficients. For 7(3^2), multiply 7 by 9.
- Exponentiation: This operation is crucial for finding the values of terms like 3^3 and (-3)^3.