20 Answer: a₁ = 4
<u>Step-by-step explanation:</u>

21 Answer: n = 13
<u>Step-by-step explanation:</u>

22 Answer: n = 5
<u>Step-by-step explanation:</u>

Finding the perimetre: 7x+4x-3+x=12x-3
Good luck!
The missing coefficient of the x-term after finding the product of (-x - 5)², is: C. 10.
<h3>What is the Coefficient of a Variable?</h3>
The coefficient of a variable is the numerical value that comes before the variable and multiplies it.
Find the product of (-x - 5)²:
(-x - 5)(-x - 5)
-x(-x - 5) -5(-x - 5)
x² + 5x + 5x + 25
x² + 10x + 25
The x-term is "10x". The coefficient is: 10.
Learn more about the coefficient of a variable on:
brainly.com/question/16895867
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