Answer:
x² = -3
Step-by-step explanation:
In algebra, the goal is always to isolate the variable, so its value can be determined.
Step 1: Subtract 21
7x² = -21
Step 2: Divide by 7
x² = -3
Step 3: Check
7(-3) + 21 = 0
0 = 0 ✔
Step 4: Answer
x² = -3
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