Step-by-step explanation:
Step 1: Add 2cos(x) to both sides
[tex]7cos(x) + 2cos(x) + 9 = -cos(x) + cos(x)[/tex]
[tex]9cos(x) + 9 = 0[/tex]
Step 2: Subtract 9 from both sides
[tex]9cos(x) + 9 - 9 = 0 - 9[/tex]
[tex]9cos(x) = -9[/tex]
Step 3: Divide both sides by 9
[tex]9cos(x) / 9 = -9 / 9[/tex]
[tex]cos(x) = -1[/tex]
Step 4: Find x
[tex]cos^-^1(-1) = x[/tex]
[tex]\pi = x[/tex]
Answer: [tex]x = \pi[/tex]
