Question

Algebra 1 Writing Standard 1: Write arguments to support claims in an analysis of substantive topics or texts, using valid reasoning and relevant and sufficient evidence. Problem: f(x)=2(+ 5) - 4 Evaluate: Prove: f(-2) When Kylie completed this problem, he did the following work: f(-2) = 2 (-22 + 5) - 4 f(-2) = 2(-4+5) - 4 f(-2) = 2(1) -4 f (-2) = 2 - 4 f(-2) = -2 Claim: Is Kylie correct? Yes or No Reasoning: Explain your answer by justifying how you determined if she was correct or not.

Answer 1

Evaluate;

$\begin{gathered} f(x)=2(x^2+5)-4 \\ f(-2)=2(-2^2+5)-4 \\ f(-2)=2(4+5)-4 \\ f(-2)=2(9)-4 \\ f(-2)=18-4 \\ f(-2)=14 \end{gathered}$

Kylie was not correct

At the point where she wrote down "negative 2 raised to the power of 2" (line 2 of our own solution), the result should have been 4, and not negative 4.

When a negative number is multiplied by another negative number, the answer is always positive. Hence whenever we have a negative number raised to the power of two, the answer is always a positive number.

Her next line now had "-4 + 5" instead of "4 + 5"