Question

solve the inequality $x + 3 \leq -1$.
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$$\begin{align*} x + 3 &\\leq -1 \\\\ -3 &\\ \\ -3 \\\\ x &\\leq -4 \\end{align*}$$

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subtract 3 on both sides.
you subtracted the same value from both sides of the inequality.
that means $x \leq -4$ is the solution set of $x + 3 \leq -1$.
test a value included in the solution set.
$-4 \leq -4$ true
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$$\begin{align*} x + 3 &\\leq -1 \\\\ -4 + 3 &\\leq -1 \\\\ \\square &\\leq -1 \\end{align*}$$

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substitute $-4$ for $x$.
simplify.

Explanation:

Step1: Simplify the left side

Calculate $-4 + 3$: $-4 + 3 = -1$

Step2: Verify the inequality

Check if $-1 \leq -1$: This is true.

Answer:

$-1$