Is a sinusoid a function whose values repeat based on position of a point that moves around a circle

  yes

Step-by-step explanation:

One way to describe a sine function is that it is the y-coordinate of a point on the unit circle that is θ radians counterclockwise from the x-axis:

  y = sin(θ)

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Another way to describe the sine function is that it is the solution to the differential equation for undamped "simple harmonic motion."

  y'' + y = 0; y'(0) = 1, y(0) = 0

  y = sin(x)

given the equation is 8+9z=-6, the first step would be to subtract the 8 from both sides:

8+9z-8=-6-8

since 8 minus 8 = 0, this would cancel out the 8. and since -6 minus 8 equals -14, the equation would look like this

9z = -14